It annoys me to no end when a web application prevents me from being able to paste content into an input field, or copy it out. If I paste an incorrect email address, that's my own damn fault. I use tools like 1Password to remember all kinds of things for me, and it's actually more error prone for me to type out all the characters than it is for me to copy from 1Password and paste into a text box.
This is a dead simple Google Chrome extension that removes copy and paste blocking.
There are some sites that do helpful things with copy and paste events, and for those sites you want their paste event handlers to still work. In the options for this extension, you can add an exclusion pattern that matches the site's URL, which will prevent this extension from running on that site, and thereby allowing the paste event to occur.