Up to now I have had a lot of issues trying to synchronise contacts with Google Contacts.

- I have lost contacts in the phone that didn't have an email address and weren't present in the GMail account.
- When more than one phone was available for a contact, I got duplicates of contacts in the phone with different types of phones than initial. For example a "work" phone turned into "mobile" phone.
- Google Talk accounts converted to Jabber accounts in the phone.

I have not tested latest versions (I'm a bit scared after the initial trials) But I will give it a new shot (after a complete backup of course).