I run a few things on Fedora (RedHat). Hydrogen, which is similar to FruityLoops. I use Timidity which is nice for converting MIDI files to waves. I've picked up several soundfonts that I used. Csound works nice on Linux. All the good stuff, like Ardour and Rosegarden...well, I'd have to recompile my kernel (for Jack) and I can't really do that on the machine I have as it's in constant use for work. One of these days I'll set up a linux box just for audio.
Just a few weeks ago, on a lark, I went to Planet CCRMA and followed the simple (haha) instructions to convert my spare RedHat 9 machine to a DAW. I think it took all of 3 hours from start to finish. (Of course, there has been a bit of tweaking here and there to make everything work! ) I was overjoyed to find that ALSA now supports my M-Audio Audiophile soundcard. It doesn't get any cooler than this.