By forcing us to adopt the two-column approach imposed by the skeuomorphic design, Apple is effectively deprecating groups as a feature. They are still there, but using them has just become much more painful. You cannot see groups or select one at all while you are viewing the contact details of a specific card. You first have to click on the red bookmark button at the top:

Information that is synced
On Mac OS X 10.6 (Snow Leopard), only contacts in the My Contacts group in Gmail are synced. On Mac OS X 10.5 (Leopard), all Gmail contacts are synced.

The following information is included when syncing to Gmail:

People's names and job titles
Company names
Email and postal addresses
Phone numbers
IM names, including the type of service
Notes
Photos (on Mac OS X 10.6 only)

With the Snow Leopard update (10.6.4) that Apple pushed out earlier this week, they released a problem that not many people have yet to realize: Google Contact Sync (GCS) is broken. I actually stumbled upon this information when working with a client earlier this week and set time aside to find a solution. Once updated to 10.6.4, you can still go into the Address Book preferences panel and enable GCS but it won’t actually save that preference. If you quit Address Book, open it again and travel to the preferences, you’ll notice that your GCS settings have been removed.