This comes from the MacOSXHints.com site.

The start time in  iPhoto '09 can take minutes if you have a really large database of photo (like 30k plus). But even if you have a small database, this will still speed up your launch time.

How To

Open Terminal and type:  cd "~/Pictures/iPhoto Library"

Then execute the following command: for dbase in *.db; do sqlite3 $dbase "vacuum;"; done

 

That's it! You should notice an improvement in your startup time.