When going through images with the ribbon at the top in iPhoto, simply press the w key -- it will get rid of the menu bar and the dock, and you can maximise iPhoto fully. This can also be done in fullscreen mode.
[robg adds: Interestingly, if you fully maximize the window, then press w again, you'll have an iPhoto window that's stuck under your menu bar, at least until you press w again and move it.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060827054554756