Sounds like there could be a database issue in the Library. Add some specific events recently? Quickest and least messy way to determine this is to pull the iPhoto Library from ~/Pictures to the desktop. When you launch iPhoto next, create a library, see if it also hangs up. If yes, its an issue with the application or its settings (plist). If not, you can dig around in the original library package for the most recent imported event(s) and pull them out. While you could try an automatic rebuild but more likely than not if you have to take this step you'll have to go the distance and do a manual rebuild, which is described in the additional information section of the linked article.
