I noticed this myself this evening when accessing my shared iTunes library via Front Row. No album artwork whatsoever, and there seems to be several threads on the Apple Discussion forums about this compared with the old version of Front Row.
I really hope this is a bug and they fix it soon as it was really handy having just being able to stream from my main computer and have all the artwork available.
Happening to me as well. Anyone else having this problem (which would be everyone who uses networked files I would guess) should add their voice to the Apple discussion board. It could be that Apple will listen.
This is a bummer for me since I use Front Row for all of my music and other media on my TV and have all of my files stored on a different computer.