According to this there are issues with restoring large amounts of data with Carbonite.
http://www.olindaservices.com/2009/11/c ... s-my-test/
Carbonite suggests Average restore time's http://cp-carbonite.kb.net/display/4n/k ... tab=search
One of the reasons to test out your restores regularly is so that you can avoid the long restore times (if it becomes an issue to you).
If long restore time is an issue, perhaps you need another backup strategy?