Hey:

I use the Fatso across the 2-bus here and there. Obviously it really helps digital recordings, but i definitely try not to overuse it. I know a few mastering guys who use it pretty consistently of digital mixes, and they swear by it.
Its different beast than the distressor. i wouldnt strap a pair of distressors on my 2-bus... you probably wouldnt want that much color on your final mix. The fatso has compressors built in side, that are similar to the distressors, but very limited in terms of manipulating it.
I love the thing, it works great on bass, and drum mixes too... if you have the means... get one!

-Mark

I ran a set of mixes through the Fatso and sent them to Bob Ohlsson to hear what he thought. He said to run just the kick and snare through it rather than the whole mix, because he loved what it did to the kick and snare.

I use it all the time tracking bass, electric guitars, drum subs and vocals. Love it.