There’s been a flurry of discussion on the Pure Data developer lists about how to tweak the sound synthesis program to run well on the Raspberry Pi. Shawn Greenlee got his Pi working and has a video up on Vimeo showing some patches running. It looks like he’s using an inexpensive USB sound card for output, but others have had success with the HDMI audio out from the Pi as well. It seems like the analog output still needs some work on the driver side, as most people seem to get choppy output after a while.
This seems like good progress though; I’ve always thought that sound synthesis (and Pure Data) is a kind of killer app for these tiny cheap embedded Linux computers.