Hi!
I really don't have much experience with the sort of device you are building, so I guess my opinion is a bit weak on this one. But for what its worth, it looks pretty good to me. All the standard decoupling caps, generous power/gnd plane, and a good layout. I always try to make things as small as possible, but thats just bad habit on my part, considering most things need to be housed in something, with mounting holes etc..
One thing, I've quickly read the PIC18F258 specs and even though its 40MHz, can it really handle the USB? I suppose with mp3's streaming in real time, that ain't a problem.
Good luck! I might post a dev board I designed for CPLD's in here at some point, when I get the board and test it.
Buriedcode