On the Apple's Discussion Forums people are reporting issues of losing data, when upgrading from iPhoto '09 to iPhoto '11. Specifically, some people are losing some or all of their photo libraries when upgrading. Also, iPhoto '11 drops support for older Apple TVs as well as photo calendars.
So, back up your photos and videos before doing the $49 iLife '11 update.
If you're having issues, you can repair permissions in the disk util:
Try deleting the Delete iPhoto Pref File
iPhoto preference file, com.apple.iPhoto.plist, that resides in your User/Library/Preferences folder.
NOTE: If you're moved your library from its default location in your Home/Pictures folder you'll have to point iPhoto to its new location when you next open iPhoto by holding the the Option key. You'll also have to reset the iPhoto's various preferences.
Then backup the library and launch iPhoto with the Command+Option keys depressed to rebuild the library. Select the options #1, #2 and #5.