I am also seeing a massive frame rate drop. Although I am on a low end machine, the game was still very playable *before* the patch. Now it is borderline unplayable. Framerate is now below 20 fps consistently and often dips to unplayable levels...FIX!!!!
Update: Believe it or not, updating my drivers worked...I know that isn't working for most people, but it did for me. I am playing on a POS low-end machine (ACER laptop) with a NVIDIA GT130M....I installed the drivers available from the ACER website (I"m sure they are nowhere near as current as the latest NVIDIA reference drivers), and my framerate was back to normal. According to the NVIDIA control panel, the version of NVIDIA drivers installed is: 187.71. DxDiag reports the drivers as 8.16.0011.8771. Again, this is the version that is currently working for me, not the version I had problems with (I didn't get a snapshot of that before I updated it).
The dxdiag posted in spoiler below is the version that seems to now be working for me.