For a while now I've been mildly irritated at the JPG files iPhoto's export feature produces. They've always seemed way to large, and I just chalked it up to poor JPEG compression routines. Since this is a hint, you must already realize I was wrong. It turns out my images had embedded IPTC profiles (short version: image metadata). I'm not sure if my camera or iPhoto embedded the profiles, but I wish iPhoto were smart enough to strip this out when you export, particularly when you export for use on the web.
Fortunately, ImageMagick comes to the rescue again. You can strip the IPTC profiles from an image by using the mogrify command:
mogrify +profile iptc filename.jpg
The reduction in file size varies, but I've shed anywhere from 20KB to 100KB from an image.

