Back Up Before Installing iPhoto ’11!
Our friend Liz Castro reports that when the new iPhoto '11 (which hasn't arrived here yet) attempted to upgrade her iPhoto Library, it failed in such a way as to delete 230 GB of photos. Others are seeing the problem too, so you should either avoid installing iPhoto '11 until there's a fix from Apple or make sure you have multiple backups before installing. It's also probably best not to interrupt the upgrade process, no matter what.
"...avoid installing iPhoto '11 until there's a fix from Apple..."
So if I have the iLife '11 disk, how do I install the "fix" (which I assume would be a .1 revision software upgrade) without installing the original disk version, which has the potential to delete my photos? Seems like a Catch 22.
No, the installation process is separate from the upgrade process. Just install iLife '11, but DO NOT LAUNCH iPhoto! Then get the 11.0.1 version, or whatever it is, and only after you've installed that do you launch iPhoto.
Apple told Liz Castro yesterday that there's an update coming very soon.
http://www.pigsgourdsandwikis.com/2010/10/wait-to-upgrade-to-iphoto-11-apple-says.html
A post on MacInTouch today describes one possible cause of deleted iPhoto libraries, though, perhaps, not the sole cause of such catastrophes.
David Ticzon's post (at http://www.macintouch.com/readerreports/ilife11/index.html#d28oct2010 - scroll down a bit to read it) describes how iPhoto plug-ins were the cause of his woes, and that an Apple engineer confirmed this. He also mentioned that doing the conversion in Safe Mode (hold down Shift during iPhoto startup) might also make the conversion safer.
Apple released a fix for the iPhoto '11 (a.k.a. iPhoto 9.0) library upgrade problem yesterday. The 33.87MB iPhoto 9.0.1 updater is available at http://support.apple.com/kb/DL1322
Apple also has released a support document that describes the problem that the updater fixes with advice for how to avoid the issue: http://support.apple.com/kb/HT4431