2.1 Contact Info Lost Problem - PLEASE READ
I have read a lot about people complaining about losing contact information after the 2.1 update. The problem is not a 2.1 problem.
When you accepted the update it warned you that there would be information you would lose. For instance, your scenes would be lost. This is what I am finding for most people that are complaining about losing contacts in their phone after the update.
This goes back to the issue that google contact syncing is one-way in 1.5. In other words, you could enter contacts into your google account and they will sync to your phone. But, contacts entered into your phone do not sync back to your google account.
So if you had contacts you entered into your phone in 1.5, and never put them into your google account, then yes you probably lost them. Always enter contacts into your google account and allow them to sync to the phone. That way they'll always be backed up (in google) and future factory resets won't result in contact loss.
Hope this helps at least one person!