As the title says.
For some reason on other forums can remember and auto login mobile devices, this is incredibly annoying due the amount of e-mail addresses and passwords everyone has these days.
It often stops me bothering to reply or help someone out with critical information (less related to this site and more to motorbike mechanical forums) because of the hassle of trying what you thought was the correct login a few times then getting locked out then having to reset the password for something else that will inevitably be forgotten!
I hate the websites that force you to choose a password with one upper case letter, at least two lower z's, a bunch of numbers forming a pythogorean triplet and the remaining characters in wingdings.