Use formatters, but make sure they work.

These are often very problematic when using a screen reader. If you absolutly need to mask an input, Filament Group has a good approach: https://www.filamentgroup.c...

It get's even more ridiculous when US developers insist that only US usage is correct.

Examples: format of postcodes, insistence that people have a middle name, format of phone numbers, the need to fill in a state, ...

All of the above, yes. I'd like to add one: Disabling paste on password fields makes me unreasonably angry.

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.