I don't know what mouse background most of you have, but my Microsoft mice lasted at least a year before the fist battery changes. My year and a half old Logitech mouse is supposed to last two years and is still going strong.
I was appalled at the magic mouse battery life of about four weeks the first time. Since then rechargeable have lasted shorter. Anything from two weeks down to 6 days after I played a mouse intensive game!
Every time my magic mouse batts die I borrow from my Logitech while I recharge them batts. The first time it was around 80%, second around 70% and third in the 60's. So the several hours it takes to charge my batts, the magic mouse sucks up about 10% of my Logitech's batteries. Batteries which have already been in my Logitech mouse for one and a half years and was at 80%. What a difference between the two mice.
When my magic mouse dies I'll definitely replace it with a Logitech. The touch system is still a bit of a novelty right now, but weighed in with really bad battery life the only thing I find magic about it is how it makes my juice disappear in no time.