I'm using T-racks and it's great. I think it's pretty bulletproof. In other words, if it's not sounding right, it's probably because it has "operator" problems, not operational problems, if you know what I mean
You can do a lot of damage with it, as with the outboard gear it's trying to model. I will usually take outboard gear over plug-ins (who am I kidding, I can't afford outboard gear!) but seriously for compression and limiting, I really think software can do the trick. When you think about it, all "real time" compressors are reactionary. So they're never doing something that a piece of software can't reproduce. The software has the advantage, because it can build the model around the premise of "look ahead". It's applying the compression to the file. So while cheapo compressors do a terrible job of emulating the real studio gear, the T-racks software can get you 98% of the way there.
Now if you're going to use it to try to emulate tape saturation, or tube clipping within the compressor unit, then it shows it's limitations. Because after saturation point, whether it's with tape or tubes, software can only imitate, not duplicate. I don't know if we'll ever really see the day when a major studio guy dumps his "real things" for a plug in. Although I read an article where some heavy producer said he liked some optical compressor plug-in, because it was consistent. He has 4 units of his own that he's chosen among dozens, but they are very random, and if he goes elsewhere he's not bringing his along. Then even if the studio has some, its likely they're not as sweet as his are, so with the plug in you always know what you're going to get. So he makes it a point to use his outboard gear on anything that's up front in the mix, and the plug ins for everything else.
Sometimes I'll process individual tracks in there, too. I'll use just the compressor or Comp/EQ combo for a lead vocal track or something, and then load it back into the session. I've used it on snare before too, for some saturation. And while it's not perfect, hey it's only the snare drum.
But seriously, the saturation deficiencies of software modelers are more noticable on tones than percussion. Its really a great all around program. You'll get more use out of it than just mastering.
