Always mouse right unless that hand is full. If I need to use the arrow keys, I’ll use whatever hand works better–right when web surfing, left when playing games that also use a mouse.
Another slightly related addition…
One user I worked with actually used her mouse upside down. In other words, she turned the mouse so that the buttons (and wire) pointed toward her, instead of away from her. She said that was how she learned to use it, and it felt most comfortable for her, but she had a hard time remembering that the “left” button was on the right side, and vice versa. She was very grateful when I showed her how to reverse the buttons.
When I first learned CAD it was with the digitizer on the left but since then I’ve always moused and balled… trackballed, with my right hand.
Ditto.
I am right handed at everything with one exception, I shoot a rifle left-handed.
Left Hand Black.
I’ve used my left hand for eating utensils since I was 10, just to be contrary, and have since forgotten how to eat right-handed. :smack: Write right and mouse right though. My father is left handed but also mouses right, since that’s the side the mouse has always been set up on.
It’s nice because I can surf message boards during mealtime with the mouse in my right hand and a fork or spoon in my left. 
As long as typing is not required, of course.
Never. I’m completely left stupid. Anything requiring any kind of dexterity is lost on my left hand, except typing.
It’s the reason I chose the trumpet over the saxophone.
I am a righty who mouses lefty. I used to mouse with my right hand, but then I started to develop some tendinitis, so I switched it to the left to give my right hand a break. It took a few days to train my left hand, but now I mouse lefty just as well as I can righty. It turns out that I prefer to mouse on the left, I use the numerical key pad quite a bit and it’s much more efficient for me not to switch back and forth between the keypad and the mouse with my right hand.
Several years ago I developed tendonitis or some such thing in my right forearm. I started mousing with my left hand at work and that helped. I never switched back. The buttons are set up righty but I mouse lefty. I mouse & trackpad at home with my right hand.
One thing I just noticed is that when I mouse lefty with the buttons set up righty my hand sits diagonally across the mouse and my middle, ring, and pinky fingers rest on the mouse pad, so there’s less tension in my forearm.
I do both.
I mouse left at work, so that I can keep the space to the right clear for writing. Also, as gardentraveler commented, it’s less strain on the wrist.
Mouse right at home, since the desk is smaller and doesn’t have room for left hand work.
What do all you people mean by eating left or right? 
I used to mouse with my right hand (I’m right handed), but because of the angle I sit at my computer at home, I had to switch to the left to reduce the strain on my right arm.
I also switched the buttons. I have the same set up at work, too.
I gave myself tendonitis in my right hand by clicking too much while teaching software apps. I had to switch. At least now I can type without getting pain. Mostly.
I still can agravate thing by using the computer too much. Occaisionally I have to ice something down.
Yeah, sometimes I mouse with my left hand, when my right hand is busy with…other stuff 
Me too. I’m strongly right handed. My left hand isn’t good for anything.
Right-hand mouse only, since it’s a right-hand mouse. I also have a Belkin N-52 on the left, programmed to function as a mouse (with cursor movement, click, double click & command click [more useful to me than control-click]), open/close, page up/down, home/end, left/right/up/down arrow and a couple dozen file, application & webpage launch keys.
Yes, I do have too much time on my hands.
100% righty, but left-handed mouser (for non-games). Not because of tendonitis, but simply finger pad soreness of gaming and computing on the same finger. So using both balances the load.
After four years, right-handing for normal tasks seems awkward.
Righty who mouses on the left (buttons are the same - middle finger for click, index finger for right click).
Several reasons for this - at my old (favorite) job, my desk was set up for computer on the left, and the phone on the right - I could grab the phone with the right hand and write down messages with my right hand, and mouse through the databases with the left, and still keep my body aligned so I could see who was coming into the office (big problem with cold-calling salesfolk and street people).
Also, it drove my first boss (MAJOR unadmitted problem with OCD there, folks!) beserk. I was the one at my desk for 8 of the 9 hours per day, set up the way I was comfortable (since I had the lion’s share of time at it), but I could tell when she was at my desk because the entire place was reset to “her” liking. Thank the gawds she left and my new boss was also a righty-writer-but-lefty-mouser.
both right and left; just switch when my hand gets tired. video games i can only mouse with my left. wasd, what’s that? i use the little arrows on the keyboard on the right. 
Totally right-handed in everything other than mousing.
I mouse lefty with the buttons unswitched (middle finger=click, index finger=right-click).
I started with computers long before mice (or PCs) were invented. When mice started to appear in the middle DOS days I was doing a lot of Lotus 123 programming. That entailed a lot of numeric pad entry back in the 88-key keyboard days before the inverted-T dedicated cursor controls.
When I got my first mouse I noticed my right hand was doing regular keyboarding, cursoring, and numeric data entry, while the left was idling a lot of the time. I put the mouse on the left so I could navigate lefthanded while doing numeric data entry with the right. It was awkward as hell for about 2 days until my hand got smart; then it worked fine and sped things up a bunch.
Here we are 18 years later.
As an aside, does anyone know of a good source for truly left-handed trackballs & mice? I use a symmetrical mouse now, but would like to get a more ergonomic one. Everything I see is molded for a right hand, despite the ad copy that says it works for both. Even Google comes up with not much to pick from. This lefty mousing is my sole experience with being a minority and it sux.
No.