FInally I solved it…
First I activated iCloud and here the problem got from big to even bigger… I had every contact duplicated on my mac because I had it both on my mac and on iCloud… I haven't quite well understand why iCloud is so poor with some features… Can't you just have the contacts on iCloud which are the same as your mac instead of having two groups?
At this point I tried to find duplicated cards to merge the et voilà…It creadet a smart group with the merged cards so now I went from having two cards for each contact to having three for each! And I could even delete this smart group…very smart! Thank you mother Apple for this… As if the Lion Address Book ugly interface wasn't enough…
So, here's how I solved the second problem and the first (iphone and macbook not syncing anymore):
I did a backup of this folded:
my_user/Library/Application Spport/Address Book.
Then I disabled iCloud sync for Address Book both on my mac and on my iPhone choosing to get rid of the contacts.
At this point I deleted the folder my_user/Library/Application Spport/Address Book which I had already backed up (and don't forget to do that!)
I then started Address Book and the above mentioned folder got created again. I got read of the default contacts (Like Tim Cook card…) and I closed it.
At this point I copied back the folders Metadata and Images from my backup of my_user/Library/Application Spport/Address Book to the original folder plus the AddressBook-v22.abcddb file.
I then started Address Book back finding all of my contacts with only one card for each (iCloud problem solved!)
Then I plugged my iPhone in (which Address Book was empty at this point) and selected the option on iTunes to sync Address Book. I synced and everything got back to working fine again!
Thank you Apple for making things easy! For sure you made me think differently today…