Same with me, and I also have a Google Nexus S. It's like I only have 1 out of 10 songs on my smartphone (might be even less), really frustrating! I hope they're going to do something about it in the near future.
There's another problem : the songs are organised in a super weird way, for example there's [Artist] > Music (which is not the album's name!) > [various songs from other artists which are not organised this way on my PC]
Anyone has the same problem and/or an answer ?