OK, so I decided to go check it out, and it followed me home. I had read a lot about it on the Internet beforehand, and it (or the Jazz Chorus series) appeared to have attained something of a cult status, with many calling it "the best solid state amp ever". I've spent a couple of hours abusing it now, and even though I've tried far from every amp out there, I wouldn't be surprised if those people are right.
First of all - the distortion sucks ass, but I've got three or four distortion/overdrive units so I don't really care. Second of all - the other built-in effects kick said ass. Given that this is a Roland amp (the mother company of Boss) there might be similarities in cirquitry to early Boss tremolo and chorus pedals. However, I'm not even close to being qualified to open it up and judge for myself, so I'll leave that to people in the know. But it definetely sounds good. The dephth produced by running my CH-1 together with the amp's chorus was stunning.
What this amp is famous for is the incredibly clean reproduction of whatever sound goes into it. It's used not only by guitarists but by keyboard/synthesizer players as well. The cleanness makes it a perfect amp for those who use a lot of effects pedals, as it lets every single one of them shine through. I've tried this with seven pedals in a row, and it worked out perfectly. Plan to add even more in the future.
Don't know what more to say. This is a killer amp for the money (I paid around $220), and it is now officially my primary amp. I'm selling my tube amp (Carvin VL100) immediately, and I'm not joking around here. The Jazz Chorus has everything I'll ever want.