I have one, and am fairly satisfied with its SQ as a portable music player. I use it for now with a Koss KSC75T, same cans I used on other smartphones before.
IMO, and this is kind of surprising out of RIM, it blows anything else I've tested out of the water soundwise, as far as portable players are concerned. Nokias (N95, E90, N81, etc), Sony-Ericsson (w910i, W960) can't hold a candle to the sound quality of this thing. No hiss to speak of, powerful and tight bass, very nice and non-fatiguing detail, it's the real deal and I don't think I'll be switching mp3 players anytime soon... It also sounds better than an iPod, which is not that hard to do.
On the Bold the music is encoded in eAAC+ @ 128kbps, which is amply sufficient for this very efficient format, and that coupled with a 16gb MicroSD card means I can take a LOT of music with me, in what is really good quality for this type of gear.
Hope that helps.