
Rebuilding the iPhoto library
Hold on Cowboy
This blog post is pretty old. Be careful with the information you find in here. The Times They Are A-Changin'
The number of photos I have in iPhoto is around 10,000. I like the new faces feature, but it just kept grinding my CPU for hours and days. I stumbled on a way to rebuild the iPhoto library, but it’s really hidden and I’ve never run across this type of a setup from Apple Software.
Essentially you need to hold down Option + Command while starting iPhoto and keep them held down until you get a window asking you what you want to rebuild. Interesting. Maybe I’ll report if solves the Faces issue with the CPU.

Reference: http://support.apple.com/kb/HT263