Just thought I'd share this - HP Photosmart Essential, quick and easy photo editing, and a free download - HP Photosmart Essential 3.5 - Free photo editing, organizing, printing and sharing software.
Universal binary, so I can use it on my iBook G3 as well as the iMac.

It is very simple, ability to organise photos, crop (which I've found Seashore can't manage), colour balance, brightness / contrast, saves in a variety of formats.
Recommended for a quick edit, use something like Gimp for more complicated work.