mine is currently set at 44100 but I recall that in 64bit we should use 48000 as the operating system runs smoother is this true?

Sample rate has no relationship with the bit depth of the OS. Nor does bit depth of the files created. 

Samplerates have a relation to the converters on your audio card. So it's really what audio interface you use. And how fast your CPU is. 48khz will be like 20% extra heavey... But with a quadcore you won't notice the additional load. But is your room like very good? If not the extra load won't give you anything sonicly in return.

Some people say plug-ins (reverb tails, etc.) sound better at 48. Don't know if that's true or placebo effect. I thought sometimes it is smoother.

For whatever the worth, CD format uses 44.1 k, while film/DVD uses 48 K.
 
At some point, higher rates chew up a lot of disk space for potentially inaudible benefits.
 
I just talked to a major studio here in Maryland, where everyone from Hendrix, Aretha Franklin, Dave Matthews, and orchestras, have all recorded, and they run almost everything at either 44.1 k or 48 k.
 
Bob Bone

There's Craig Anderton's view in a thread somewhere on this forum that recording at higher sample rates (he tried 96KHz) then lowering the sample rate at the mastering stage can improve the performance of some plugins such as amp emulators or compressors that don't over-sample because any folding of frequencies above the Nyquist frequency ends up in the inaudible range at those sample rates rather than at audible frequencies.

Having tried 88.2KHz I think he might be on to something. Then again it might be a placebo effect. Certainly uses much more disk space and throughput though.

I'm pretty sure all the British singles were 44.1, that's why they didn't appear on the US ARE YOU EXPERIENCED album. Warner/Reprise demanded 48k!

tlw
There's Craig Anderton's view in a thread somewhere on this forum that recording at higher sample rates (he tried 96KHz) then lowering the sample rate at the mastering stage can improve the performance of some plugins such as amp emulators or compressors that don't over-sample because any folding of frequencies above the Nyquist frequency ends up in the inaudible range at those sample rates rather than at audible frequencies.

Having tried 88.2KHz I think he might be on to something. Then again it might be a placebo effect. Certainly uses much more disk space and throughput though.

Actually you can now gain the benefits of 96 kHz recording with 44.1 kHz projects using the Upsampling on Render feature introduced in Foxboro.

From my experience, the best sampling rate is the one your A/D is designed for. Some A/D converters will support 192Khz, but because of the components used inside they may perform better at 96Khz, rendering the expanded sampling rate a mere marketing tool. Personally, and this isn't just my opinion, I would say anything over 96Khz is a waste. I've also concluded that, if your ultimate destination for audio is MP3/MP4, and you're not recording classical or sound-track material, 48Khz is just fine. Save some drive space. 
 
With the new upsampling processing, you really get the best of both worlds in saved drive-space, but higher sampling rate processing. Although it takes a bit for me to trust the theory and technology, I'm willing to use it if my end result is pleasant. 

Yes indeed. If there is some audible benefit to the upsampling feature, then Cakewalk has done a really nifty thing here. Probably most of us have individual plug-ins that do this, but including it within the DAW is a brilliant idea.