I always record one side with my Ibanez and the other with my Les Paul Custom. Of course, you have to be pretty good at timing.

Brian,
 
I think if you did a blind study with sims vs miked guitar in a mix, the 95% or more of people would NOT be able to tell which was which. My buddy who runs a studio tests me on this to me all the time, and done correctly, it is DAMN hard to tell. If you isolate them, it is a little easier, but not a slam dunk to be able to discern one from another IMO.
 
I have a nice rig, but actually prefer the amp sims when I play because of the versatility they provide. Especially after you capture the performance. I don't want to re-amp or run a split.
 
So the bottom line is: Get the sound that inspires a great take.

Sanderxpander
That Slipperman article made my day, thanks.

Also made my day! It's crazy goodness.

hockeyjx
Brian,
 
I think if you did a blind study with sims vs miked guitar in a mix, the 95% or more of people would NOT be able to tell which was which. My buddy who runs a studio tests me on this to me all the time, and done correctly, it is DAMN hard to tell. If you isolate them, it is a little easier, but not a slam dunk to be able to discern one from another IMO.
 
I have a nice rig, but actually prefer the amp sims when I play because of the versatility they provide. Especially after you capture the performance. I don't want to re-amp or run a split.
 
So the bottom line is: Get the sound that inspires a great take.

I won't say I've sat in a studio performing blind tests for Amp vs. Sims, but I can point out a very common situation where the amp will usually win for me. I recently recorded a band that has a guitarist using a 1978 Le Paul Deluxe (mini-humbuckers) played through an original Peavey 5150 head (6L6 tubes) and half-stack cab with Sheffield drivers mic'd with an Avantone cv12. The guitarist has been using this basic setup for about 7 years. In that time he's quite honed his tone, to say the least. He knows exactly how to get what tones and power he wants from this particular rig.
 
The last time I tracked him, about a year ago, we fed his signal into an Audient ASP008 Mic Pre direct from his guitar using a transparent mixer. One output of the mixer forwarded his signal to the amp, while feeding a perfect copy of that signal to the Audient. One signal was clean, while the other was fed into the amp and mic'd. We just wanted to really see what his signal would do through a few different amp sims and even some sim stomp boxes. Waves GTR, IK's Amplitube, and NI's Guitar Rig were all included in the lineup. 
 
What time we spent was busy indeed, in finding sounds/tones he really liked, but the main thing we simply could not find was the intense "bite" his rig had. There simply was not an easy way to fully duplicate his rig.
 
This isn't to say sims aren't useful, and they are improving all the time. However, I'm still convinced it's easier to use the real thing if you know that works and you know how to capture it vs. trying to emulate a guitarist's tone through sims that weren't modeled from his specific setup. If you have no amp at all, perhaps the sims are deadly! We just preferred the real thing.
 
Sidenote: I was at a gig recently where I could hear one of Line6's prestigious half-stack modeling amps. I believe he was using a Marshall sound, but I couldn't tell for sure. The other guitarist was playing through an Orange British half-stack. During the set, and I'll admit I'm a trained ear to the situation, but I noticed the Orange amp's presence and resonance superiority. The issue I had with the Line 6 was that, although it sounded much like a Marshall stack, it sounded as if someone recorded a Marshall stack and simply played the audio back through this Line6.
 
 
 

If you heard his tone out "in the world" first, there may be a bias there. Just as if you know someone has a Line6 vs an Orange in person, you might be prejudicial if the tone is close. A bit of a placebo effect if you will.
 
But to my point: it still is hard to reduce distortion efficiently (without re-amping trial and error) when mixing, and that is where the sims are pretty awesome.
 
We laid down tracks live at a real, and I didn't like them in the mix, so I redid them with GR5 and loved them.
 
There is no wrong or right, just what you prefer or what works for you. 

I play guitar really badly but I've gotten a few people with good ears to ask how I recorded a part, using S-Gear 2.
Not to say that I could copy someone's "real" tone, but it sounds pretty good in and of itself. In a situation where the track is just presented "as is", I believe you can get great results out of a sim.

Some good conversation. So, let me qualify something real quick. There's absolutely nothing wrong with using Sims in my ears. I'm mainly advocating that if you can do the tried and true amp, that's my purist vote. I personally prefer the real thing, however, in many cases, I'm no analog snob. My mixing and Mastering is all in the box. I just feel if you're copying or re-amping, the real amp can likely be easier to get exactly what you're looking for, IF that's where the sound is right. One could tweak to heaven and back on a sim to get the sound the amp naturally has.
 
Hockeyjx has a solid argument about reducing distortion on an otherwise clean guitar. Sims are amazing there. Believe me, on another session I have, the amp used was awful and I'd love to get rid of the Boss pedal distortion, in favor of a real tube head.
 
The thing that tube head rigs can provide that emulations can't (faithfully, IMO) is what you get when you drive the bias of a tube in different ways, such as using the Resonance setting on a Peavey amp. It creates this "loosened" effect that can be felt in the room, which simply fills the air with a solid layer of guitar. An Ampeg SVT bass amp pumping an 8x10" cab is another example that a sim simply cannot provide (at least none that I've tried). They come close, but again, there's a certain looseness or punch-iness and such you can get from a rig that inherently just fills the track.
 
The argument I have against sims is one that I believe has been valiantly fought for years--with some success. Once the signal is in the box, the signal isn't as reactive as an actual coil pickup underneath the strings. In the box, you've passed through at least a few OP-AMPs which will collectively smear the signal and then, depending on your A/D converters may not retain the full thrust of a mad guitarist ready to break strings. Even if the sim were exactly the same as the real amp/cab, the input signal has changed slightly, and I can even see that on my scope.
In either case, I use sims, too, when that's the only real option, or when the amp just isn't doing it for us. However, standing the sim up against what I can mic from the amp, the amp emotionally works better for me. Don't get me wrong, I'm excited to see better and better sims coming. I don't have any problems with post-processing a guitar if it works. I just think that doing so now is harder to me than getting the real thing in the room and tracking it there.
 
And I do have a sort of contempt for modeling amps, not because of brand or accuracy. It highly depends on the room. In a studio, both amps may sound exactly the same. A lot of effort has gone into these ideas. However, this isn't a typical result in a live room on a stage, and most live shows don't happen in an acoustically controlled room. I still believe the engineers at companies that make amps which emulate other, more expensive tube amps are clever and ingenious, but I also believe there's a sense of arrogance that these amps are better than the real ones.
 
 
 

I understand a certain level of purism. Piano is my trade, and I will (probably) always maintain that a real grand sounds better and fills the room in a nicer way than a digital emulation or sample set can. If I had a convenient way to record a real grand I would always pick it over a plugin. Still, I'm sure I've heard many tracks with VSTi pianos that I considered to be real.

I am having some really good results with the Torpedo-Wall Of Sound plugin. It was mentioned on this forum a few days ago and I tried it and liked it very much. I am using a Fender Concert-Rivera model with the line recording connected to the interface. Then in X3, I have the wall of sound plugin doing the cab sim. I have Amplitube, GR, Pod Farm Free, and TH2. I use them constantly but being able to use my tube amp without the micing hassles and also being able to change cabs is priceless. If you get a chance, check it out. The plugin is free. You can check it out with all the cab sims in their library for free. You don't like it, dump it. If you like it,they only ask you to buy two or more of their cabs. I bought 5 cabs for about $60.
Bringing my tube amps in to the interface and using cab sims has brought a really nice choice of tones in to play.

This is very good information.