UI Horror: No-Paste Password Fields
Sure, it makes sense to disallow copying passwords from a password field, but disabling pasting is just being annoying.
News flash for developers doing this (such as Intuit, in TurboTax): I'm not thrilled about manually typing my 20 character random password. Just let me copy it from my password vault and paste it into your field.
In the case of TurboTax, it diminishes the value of data import if I have to type more characters for my password than there are numbers on the form to input.