Had this issue with a few select songs and it was driving me crazy as I first thought something was getting randomly corrupted during sycning but it occured on the same songs over and over in the same place. These songs also played perfectly fine on my computer.
After inspecting the file information in Winamp (which has some amazing information by the way)
PROBLEM:
I realized the problem tracks were all music store downloaded tracks that were encoded with VERSION 8 of WINDOWS MEDIA.
SOLUTION:
This worked for me:
Force the Zune or use a another program to reconvert the songs to a newer(different) file format. I'm not sure which preserves the most quality but it'sbetter than the song skipping.