I think most just use it in the final stages with stems imported from the workhorse DAW of choice, final mixing what have you in Mixbus. From my experience, which is only short, and from what I read around the place, to do anything else, ie, treat it like you would any other DAW, with all that that encompasses, and expect all to be fine is but a pipe dream at the moment.
 
 The last time I fired it up, I did exactly that, just did a test by exporting some stems from Studio One, importing them into Mixbus, then mixing, messing around with the tracks EQ's, Comps, Saturation etc, no using VST's or anything like that, it seemed to work ok, there were a few strange things, until I shut it down. I saved then closed Mixbus, well tried to, it just froze/crashed, requiring a reboot to be able to continue with any other audio application. I can not kill it from TM, it just refuses to die, thus requiring the reboot. So after that I have decided to wait for either the next interim or official release before trying it again.
 
As for the sound, well to be honest I am yet to hear it, I have no doubt it has it as others are saying, but for me it doesn't really do anything I am already achieving via Studio One and various plugins, tape sims, saturation, EQ, Comps etc. I done a test in my last outing with Mixbus, exported the above mentioned test, just Drums, Bass, Guitars and Vocal, and compared it to the same test, which I exported the stems to Mixbus from, but (roughly) mixed and exported from Studio One, to be honest I couldn't really hear a difference, listened on Headphones, via monitors, stereo system, and if I had to choose one file over the other it would have been the Studio One file. I'd like to finally get it, I'd like to be able to hear it . . . But . . .  Before purchasing and after reading all the reports (the good ones) both here and at other forums, I had imaginings of what the sound would be like (nothing over the top mind you, realistic), but for me it just hasn't become a reality.
 
Lawrence, a very active member over at the Studio One forums (and others), and a reasonably knowledgeable and experienced person in the field recently had this to say
 

I mixed a song in the interim release version yesterday on Win 7. I love the sound and general console workflow but it crashed 3 times in about an hour... just went totally white and had to be forced quit a few times.

They're onto something really great there imo. The only issue for some (the other stuff is largely subjective) is stability. I can take a crash every other day with anything and not be annoyed but when you get multiple crashes doing basic things like just loading their reverb plugin it becomes less tolerable.
 

Pretty much matches my experience thus far, and there are many with similar and worse experiences, there are also those with good experiences, but for me the crashing, especially requiring a reboot to be able to continue is more than I am willing to tolerate, at least for this release, I will however check out new releases in the future.
 
It can, one would hope, only get better, I guess only time will tell.
 

Thanks for the input John and Richard.
I am going to wait for a while. I may too many changes (edits, tuning, arranging) in my pre-mixing to commit it to HMB. 
Studio One's project mode works great to be able to get back to the song, edit, and update, while I am mastering. That works well for someone like me that is constantly changing things. 
I am very interested in the way HMB color's the sound. I like a lot of what I have heard. 

Be sure and leave the audio system set to portaudio as default. Don't switch it to asio. Leave the driver set to asio. This was a fix they made early on and was causing a lot of the crashes. Contact me if you want to compare settings. I'm not having the same issues as you guys are. My projects open and save fine. There are a very few VSTs and Instruments that will crash Mixbus, but on it's own...it's been very solid here. I'm guessing the errors are coming from that startup page.

Great tip Clint. Thank you. I haven't had a chance to install the update yet, but when I do, I'll make sure it's set up as you said. I haven't really had any crashes with the other update though, so I'm assuming it's set up correctly.

I'm here to help if I can. Mixbus 3 does have a few bugs left, but they have been making huge strides with it. It doesn't compare as a daw to what Sonar can do, but it has a nice sound. I look at it like some do with Ozone or T-Racks. It's a nice unique sounding tool for mixing or mastering. It's also nice to be able to over dub if needed.
Someday I'm going to do a song in Mixbus from beginning to end...probably after 3.1 comes out.

I just installed the latest update a couple hours ago. I imported a stereo mix and tooled around with it for a while. I'm happy to say that my Faderport is working great in it, and I had no hiccups or crashes.

FaderPort is a little weird when you have groups. But I'm sure they will get that kink worked out (at least I hope they do). In the meantime it's suggested to turn the group off if you want to edit a track in the group.

Thanks Bapu. I appreciate the tip!

Just passing on what I learned on the HMB forum (and some personal experience to boot).

Messed with it some more tonight. I did have an instance where it hung up on closing the program. I had to end the process in the task manager. Other than that, it put a very nice sheen on a stereo mix that I imported from Splat.