Just a few tips here, but they radically cleaned up my iPhoto disk waste:
- Empty the trash - seems like a no-brainer, but I was unaware that iPhoto had it's own trash bin. Just follow the menu entry to clean out those deleted pictures: iPhoto -> Empty Trash. This got me over 9 GB of disk space back.
- iPhoto Diet - this is a very nice tool which will allow you to scan your entire library of pictures for more iPhoto nonsense (chuff, duplicates, and even more stuff you don't want to know about).