Ooo... power tools! Yeah, Onyx should be fine--I'm pretty sure it's just using the same command line stuff as Disk Utility to fix permissions.
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Ok, I've been spelunking
a thread on the Apple boards where some poor guy had an overfull hard drive and some serious iPhoto library corruption, and someone there suggested deleting the cache, in case that was corrupt. (/Users/[youraccount]/Library/Caches/com.apple.iphoto).