Why won't iPhoto open after upgrading to Lion?
I had the same problem and I fixed it. It's really a iPhoto 9.1.5, Time Machine backup/restore and Lion upgrade issue.

To fix my problem I:


Delete my iPhoto Library on my HD
Restore the latest iPhoto Library from Time Machine
Delete iPhoto software
Reinstall iPhoto with my iLife 11 DVD
Start iPhoto, but it asked me to upgrade from Internet. I did. 
With iPhoto 9.1, I started it and bingo, the issue is fixed.
After a few tests, I did another software update to have the latest iPhoto version, 9.1.5


I tried many things the past two days, but only the steps described here worked.

Hope it will help you.

Serge