I'm throwing a lot of fire magic down in my current game and have found that the flame wall spell causes my computer to hang for maybe a full 10 seconds.  I see the 'spell casting' text come up, everything freezes, then it eventually kicks back in showing the dissipating particle effects from the end of the spell animation.

I'm not sure if this was the case in 1.00 build, but I get the same issue every time I cast it.

Other than that 1.01 does seem to have improved game performance considerably.