I will have a more in-depth post very soon, but just to quickly get this out there:
If you are having problems logging in, there is some final work being done on the security system, and it should be finished within the next hour or so. You should stop seeing a "bad username/password" message when it's finished.
ALSO, passwords are now case-sensitive. So be sure your capitalization is correct when you enter your password. Also be sure that your Caps-Lock key is off.
More to come soon.....
Update: Well, it's going to take a bit more time than I thought for every single account to be processed. At the rate it's going it might take a few hours to get through everyone. But it's chugging along, so if you're seeing the error when you try to log in, just try again every 10-15 minutes until it logs in.
If you're already logged in this doesn't affect you.
Update 2: You can now FORCE the system to finish your login processing by changing your password. It is a 2-step process in which you need to receive a confirmation e-mail, and then click the special link inside the e-mail. To do this, click "Change Password" in the Options menu.