For me I prefer to buy one with a dock for charging the mouse so you're not going through batteries.
Had a trust one (£1

for 6 years then a Logitech 1500 laser wireless desktop for the past 4 maybe? Both spot on and cheap. Get one that offers encrypted signals if you're uber paranoid and live in a dense area.
Then again this reckons it has a year's battery life
http://www.dabs.com/products/logitec...200&origin=pla
If it's anything near that, the inconvenience of it going and leaving you without suddenly (temporarily) would outweigh the clutter and more frequent recharging.