Nuevasync works better than Google Sync but not perfect. If i merge contacts they don't get synced back to Google. Sometimes it decides to resync my whole contacts. Then i have to merge them all again. No good Solution. Antother Problem with contacts is that if i assign a image to a contact on the phone it also doesn't get synced back to Google.
I am not really happy with the N900 because of this sync issues. On my Symbian devices i have used GooSync. It was a good and reliable sollution. MfE tells me half the time, that it can't reach the server. Push Mail isn't working. Sometimes i have to reboot the N900 to get it syncing.
The most annoying thing is the mail sending issue if you use MfE and Nokia Messaging. Outgoing mails are always moved into the outbox of the MfE Account. I have not enabled mail sync on MfE so they never get sent. This is a known bug and i hope they will fix it. Until MfE istn't working perfect i will disable it. It's a bit annoying to manually maintain the devices calendar and contacts but it's the only workaraound available.