But then how do you cut and paste? Ctrl-Z, X, C, V are going to be hard to reach if you're mousing with your left hand.

This problem never came up for me.

I am an Emacs user with both keys either side of Space bar mapped to Ctrl. And I use Ctrl with either hand using my thumbs bent inwards (or sometimes with my palms).

I also try to use mouse minimally.

I've moved numpad to the left instead:

http://www.a4tech.com/product.asp?cid=1&scid=1&id=54

Context menu select?

With a mouse in your off hand? That's got to be slower.

Southpaw copy/paste/delete shortcuts: ctrl-insert, shift-insert, shift-del

Southpaw here. Right thumb on left ctrl, zxcv are all right under my fingers.

A friend of mine did the same to improve his ambidexterity (he's a surgeon and fine motion is important to him). I can't get used to it though.