Add me to the list of people experiencing this failure. It happened to me earlier this week: I was playing, got a CTD, and then couldn't log back in. Since I'd experienced this with World of Warcraft, I just waited a couple of minutes and tried again, and it worked. But last night it happened again, and I've been blocked out since.
Adding to the appearance of amateurishness, at least when I encountered ths problem with WoW, the error message correctly identified the problem as "Another player is logged on using that account name." Falsely telling people that their account name or password is invalid is surely creating a lot of unnecessary confusion and frustration.