iPhoto 9.4.2 crashes on startup and reboots MacBook Pro 10.8.2
This link to Apple's Support page on Safe Boot, or Safe Mode, details what what is loaded and what is not, and may point you to possible problem areas.
http://support.apple.com/kb/HT1564

But more details would be helpful. Which MacBook Pro, whether you've repaired disk, what manintenance utilities you run. Often, with crashing apps, removing its Preferences file cures the problem. Sometimes--not often, but sometimes--a fresh install of the app is the solution. 

Also check your Crash Reports for clues--and google the problem as well. Of all Mountain Lion Apple apps, iPhoto is certainly the touchiest. If you have Photostream turned on, try temporarily turning that off.