I have suffered multiple crashes from my BBM 5.00.55 so I decided to upgrade but something was acting up and then half way thru the update the phone fell and restarted which resulted in BBM disappearing from my screen.

I had to remove the software through the desktop manager and then reinstalled BBM 5.00.57 from the phone. The best and only way to really restore all contacts and groups is through your email. Back Up to your email consistently to make sure that you have the latest contacts and groups.

One I asked to restore from email it took about 20 minutes to verify the email which freaked me out a bit, then it took about 10 minutes to restore all my contacts and several hours to restore the groups which some how came through successfully. So Blackberry has a clear and good working process for restoring the contacts and groups.