I tried to upgrade to iPhoto 11 yesterday, only to find that my 233Gb of photos had been reduced to 6.5Gb, and that my 50,000 photos from the last ten years were gone. Completely. And I was not alone. Reading through the Apple Discussions Forum is heart-wrenching. Post after post from folks who have lost thousands and years of photos. I have done my level best to spread the word and make sure that people have a solid backup (as I thankfully did) before upgrading. If you follow me on Twitter, you're probably sick of me posting about it. But I love my own photos too much to not do everything I can so that no one else loses theirs.
And I guess I love iPhoto too much to give up on it. I thought a lot about whether I really wanted to try again. I even gave Picasa a cursory look as Farhad Manjoo recommends. In the end, I felt like all my public grousing at least demanded that I try again and see if I could find a solution. OK, and I admit it, I still wanted to see it for myself.
Thanks to the folks in the Apple Discussion Forums, I found a solution that worked for me. I restarted in Safe Mode (by holding down the Shift key as the computer starts up). Then I went to Disk Utility and repaired Disk Permissions. After copying my backup of my iPhoto Library back to my computer—which took more than two hours—I launched iPhoto with the Command and Option keys held down. In the alert that appeared, I chose options 1, 2, and 6. iPhoto then asked if I wanted to upgrade my library, to which I said yes.
And then I just waited. And waited. I even left to run an errand. Several hours later, it was done. And all the photos are there. I'll let you know if it was worth it.
But don't forget to make a BACKUP before you try it!