I've had the same password for some sites for years with no regrets. Meanwhile, at work, I find myself being forced to change passwords every two to three months. My thinking is that if a password gets compromised, requiring that I change it several weeks out isn't going to protect me or the network very much. Moreover, I find that by being required to change passwords frequently, I degenerate into a predictable password pattern (e.g., BearsFan111, BearsFan222, ...) which results in easier to remember and easier to guess passwords.

Is there a sound argument for requiring that passwords be changed periodically?