Anyone running Avast with today's update?
If you are, both Punk Buster executables (A and B) are being flagged as malware by Avast. Avast will not allow it to run so when you try to join a Punk Buster enforced multi-player match, you'll connect and load the game then you're booted because of it.
If you haven't updated your definitions yet, you should be Ok in BF3 (but not so much other places).
I have the exact same problem, hope it gets solved fast =(