Zune "Gapless" doesn't seem to be gapless for any LAME 3.97 VBR MP3 rips I've done via Exact Audio Copy or equivalent. WMA albums are gapless 100% of the time, however... so Zune Pass albums that have audio that bleeds between tracks are 100% covered. Some people have posted gapless success with MP3, but I'm not sure how they were encoded. Amazon MP3 is all LAME MP3 VBR, so their whole catalog might be impacted. Or maybe it's just me?
Same LAME VBR MP3 albums are gapless on iPod/iTunes, Winamp, etc.