I freaked out a little bit after my hand started twinging this afternoon (ARGH, THE DREADED CARPAL TUNNEL WILL GET ME), and tried to swap my mouse pointer to the left hand.
Everything just became... hard. I was all mixed up, and couldn't work out which mouse buttons did what.
So, I got to thinking - where are the dual mouse interfaces? Two mouse pointers, one for each hand.
Apart from Surface, I don't know of a single one. Surely there must be something out there...