When you first signup to Covve it will create a backup of your chosen addressbook. The vast majority of the details of each contact are backed up.
Some things to note that are specific to each address book type
When the contacts are restored, Google will attempt to parse addresses and split them into their various fields (country, state, etc).
The following fields are not currently backed up:
Also, the email display name is re-calculated by Exchange when the contacts are restored.