I just bought a Samsung Galaxy Nexus a few days ago, and today I've realized that there were some data sync errors. One with the Twitter contacts, and another with the browser data on my Google account.
I googled a little bit about this issue and I found that there is a bug in the last version of Twitter for Android that makes it incapable of syncing contacts on 4.0.2 (ICS) devices, and the only solution for now is inform Twitter about the issue here https://support.twitter.com/forms/apps :S
About the other problem with the browser data, I've found that Android does not support encrypted bookmarks with the browser data sync feature. So I've had to remove all my Chrome data from google.com/dahsboard and resync Chrome without encrypting the bookmarks (only passwords). I've had to do it 2 times because the first one didn't work (don't know why), but I've done it again today and now it's working fine.
Browser sync issue