The straighten tool can be used together with the Alt key to display a rotating grid. However, it is extremely slow then.
The slowness does not seem to be caused by a slow update frequency, but by the strange behaviour that the grid seems to be recalculated for every position that the mouse cursor was on its way across the screen: The mouse positions seem to be "buffered" - when stopping mouse movement, the straighten tool "plays back" the last mouse movements for a few seconds.
LR 4.1 64 Bit, Win 7, Logitech G500 mouse with no special driver installed (vanilla Win7 driver). Mouse sensitivity is set to medium, but the behaviour is the same for low and high.
EDIT: I see the same behaviour with the "Wacom Bamboo Fun Small" tablet, also with no special driver installed. So it seems to be a general problem and not related to hardware or setup of my PC.