I only time I've had problems logging in is when I forget to turn my ALL CAPS off and type in my password in capital letters instead of lower case. Since I can't see the password entered, I don't know it's in caps until it tells me the user name/password combination is incorrect.
Yes the site was down for maintenence for one day, but there was a notice when you tried to log in to that effect. It was down for less than a day. I was able to log on later in the day (of the day of maintenence).