One thing I find myself using FAR more than I ever thought i would when I got it, is Ulead Smartsaver Pro plugin for Photoshop/Paint Shop Pro.
Back in the day it was useful to save storage space, and make high res images just small enough file size that my email provider wouldn't reject them, but in more recent years it is great to use to tweak something posted to forums so it is as high quality a pic as possible while just small enough file size to not be rejected... then again I am sometimes thwarted by forum code that assumes a pic above certain dimensions is automagically too big, so the forum code resizes it smaller dimensions, sometimes at an increase in file size. DOH!
This is especially true in some of the more technical forums I participate in, where there are diagrams you kinda need to be able to read the text on, but don't need a 24+ bit palette so some bits can be saved without useful visual information loss, going 8bit, optimized palette PNG. I use JPG a lot less than I used to.