Apparently Imageshack drops images after the passage of some unknown time span....which is why some of us are now using a different service.
I too have switched to a Photobucket account, and replace Imageshack-hosted images with Photobucket images as required. If you find a missing illustration in any of my old posts, bring it to my attention please.
It happened to me, too. It appears that Imageshack went from being "free" to being fee based. If you didn't "pay up" your images were wiped from the system. I also have a PhotoBucket account. I've been slowly switching over. Like Dan, please contact me via email [click on my user name while signed in] or private message if you find images missing from my posts. I'll do my best to fix the problem.
Charlie