So this has been happening for awhile, but I used to be able to get past it after a couple attempts. It started around Wed, when the rose regalia update started.

SK window opens fine, login works fine.
Clicking on a character never brings me to the ready room. It posts the "entering ready room" message on the bottom.
Closing the window and restarting the client starts up the client "Spiral Knights [knight name]" indicating that I have logged on and the game crashed [It doesnt bring up the character screen].
Hitting options gives me the option to go to haven. Sometimes hitting go to haven actually allows me to play. [Sometimes I need to restart the client another 4 times before it works].

This is a steam-enabled client, for reference.

[Solution]
Steam had a bad patch for overlays on openGL games, which was fixed.