if you use gallery (as i do with gallery.mcgheemail.com) and you run into disk space issues, check out the new version of gallery (1.4.1) which enforces maximum sized image uploads (so people can upload huge files straight from their camera and it will only store a reasonably sized copy on the web) and myresize.php (thanks to beckett)
this allowed me to take a 350M site (limit was 333M, whoops) and shrink it to 267M. not a huge difference, but enough, and now all the images are still quite big, but not ridiculous.