I had the same problem. I did the import on almost 11.000 users (and it was a pain, since the server always timed out!) and they can´t login.
The password field used to be plaintexto too.
I will not go over the import process again, since I had to do it for each letter. So I´m choosing to let the users retrive their login via the password remembering page.
The problem is... The "Forgot your password" link is not showing up!!! Why ?
Do I need to activate it somehow by a forum config ? It´s a brand new wwf 9.5 instalation.
Any help ?