there are problems if you use pwnagetool and pwn your phone after you upgrade to itunes 8. If you have previously pwned your phone before you upgrade to itunes 8, then just do an (option/shift) restore and add a custom firmware that pwnagetool provides for you. if you pwn after upgrading to itunes 8 (like me) you will get a 160x error message. BUT an easy fix for that is to just use quickpwn, which does not use itunes at all.
ALSO, there have been some errors like 13213 when you try and sync for the first time when syncing the GENIUS playlist. an easy fix for this is just to try rebooting your phone and computer
Hope this helps, if it does, try hitting that thank button
cheers,
Mr B