I've had my wireless mouse and keyboard for about 2 years now, with no problems. I only vouched for wireless because I wanted to eliminate as many wires as I could in the back of my computer (they're very annoying when you have to constantly pull it out to work on it). I've had the same batteries in these things for practically as long as I've owned them
Also, it's funny that you mention the whole dpi and photoshop thing, because I bought a laser mouse and I did notice it was considerably easier to move the lasso tool smoothly in photoshop. In my school they have optical mice that seem cheap, and I have a hard time keeping the cursor perfectly steady when working in photoshop. My mouse is only 1000 dpi, which is fine for me, but I bet if I got a much higher dpi mouse, I would probably notice it being even easier to be accurate with the lasso, as well as other tools in photoshop.