I'm left-handed and use a right-handed mouse, but not all of us are comfortable using the mouse with our non-dominant hand. If the comments on this page are any indication, a left-handed Naga mouse would be a boon to more than a few people.

As for pens, a lot of we left-handers tend to drag our hands over what we've just written as we write, and if the ink doesn't dry quickly, it can smear and/or get on the sides of our fingers. I've ended up with black, blue, and/or graphite marks on my hand all my life. I'm pretty sure left-handed pens just have quick-drying ink.

I used to have a left-handed fountain pen. Nibs tend to work better when they're dragged rather than pushed, so the left-handed one had a nib that curved slightly to the left. I guess there could also be a left-handed biro that somehow worked better when pushed.

I have no idea why scissors don't work when I use them in my left hand, but it's true - they don't.

bth, I'm leftie and have just been using a right handed mouse for like, ever. Can't do leftie mice.

I feel that I am better off pressing keybinds and such better, than using a mouse designed for lefties.

But well, not my decision.

p.s. - leftie scissors are awesome

http://www.anythinglefthanded.co.uk/acatalog/yoropen_set.html
I have these, but there are a few different types. You hold the pen normally, and it puts the point out so A) You don't drag over it with your hand (yay hand smears), B) You can see what you're writing as you write it, as opposed to it being hidden under your hand, and C) like stated above it causes you to pull the tip more then push it.
I love it, and it is funny watching others try it for the first time, especially righties. :P