Bumping this as I also have the same issue. I have been playing since launch perfectly smoothly on high settings with an average of 45-60 fps. I logged in today and got a startling 10 fps in a zone with little to no activity..
Geforce GTX 570
There has to be something in the latest patches (those random files we download everytime we log in) from the last day or two that really screwed it up.