My game http://www.pasteall.org/blend/19904
(feel free to make into your game 
)
runs TERRIBLE on 2.66 on my machine but fine on 2.65
???
try it, on 2.65 vs 2.66
60 fps 2.65
6 fps 2.66
this is a issue for me, as the game works for me right now in 2.65 fine
your build is much much cleaner
I had not went back and applied any decimation etc yet on that, as I had not learned about efficient CPU/gpu practices yet,
If this is a reproducible bug, you should submit it to the bug tracker with an attached .blend file.
Ok submitted
Are you sure this is a bug? Have you reproduced it yourself with another blend file. From what Josip was saying, it sounds like you were calculating too much useless physics. I tried the file on both 2.65 and 2.66 and got terrible FPS for both (around 10-15)
You should have posted the bug in the bge tracker instead of the general tracker, but I’m sure someone will move it.
You can download the fixed version from my first post and see the fps difference. Also if you enable profiler you can see that physics kill 99% of the framerate
I got your version, but the thing is, there still was a difference with my file,
I am not sure what they changed, but it might help them not screw up some one else’s game,
you version is indeed much more polished,
the devs got back to me almost instantly