Jakob Nielsen says "Stop Password Masking"

When you’re logging onto an account, on the Web, you’re used to seeing bullets replace the characters as you type your password.  This has long been thought to help with security, however, Jakob Nielsen, a world recognized authority in Web usability just published an article called Stop Password Masking.

Nielsen states that this is a usability problem, that it does not help security, and that it actually increases business cost due to the amount it takes to address login failures.

Summary:
Usability suffers when users type in passwords and the only feedback they get is a row of bullets. Typically, masking passwords doesn’t even increase security, but it does cost you business due to login failures.