Some wireless mice experience a little bit of lag (e.g. moving the mouse and seeing the cursor move a split-second later). They bug the hell out of me. I have a wireless laptop mouse that has a little bit of lag, but I don't mind too much because I don't use it all that frequently.
On the flip side, I just bought a
Logitech MX1000 and there's no lag. By the way, using the MX1000 is like heaven for me.