I’m right there with you on removing the trailing space from email addresses. So frustrating.
My favorite thing to complain about is limiting what keys can be pressed in a field. I love my Text Expander snippets, but they can’t work if the field (like phone number) doesn’t allow letters to be typed. The worst example of this is AT&T business wireless site that filters out meta key combinations. They do allow cut/copy/paste, but ONLY if you use a Windows machine. Their javascript checks for Ctrl-<key> but doesn’t allow for ⌘-<key>! After much bitching, I created a Greasemonkey script to completely disable javascript on that particular field.
Oh, another one I forgot about:
Kohl’s credit card site insists that your payment amount have a decimal and 2 number following. They apparently can’t figure out that when I type $x that it means the same thing as $x.00!
Now get off my lawn!