There is a notorious bug in iPhoto. If it bites you, you'll never be able to empty trash again (or at least until Apple fixes the problem, outstanding for 6 months now). iPhoto simply crashes. The problem is described here, as is my solution using iPLM:

http://discussions.apple.com/thread.jspa?messageID=2770179#2770179

iPLM is indispensable. I mostly use it to assure the integrity of my iPhoto libraries. Until the iPhoto Team gets its act together wrt. fatal database corruption, I won't be able to live without iPLM. Then again, maybe one day I'll bite the bullet and move all my photos out of iPhoto to another application!