Hepp!
He he ... yeah.. I've given up on this forum mostly, people here seldom answer anything except it's been reviewed on THG, which is sad. But anyways.. I used an MX700 before I bought this desktop, the RF technology is ok but the range really sucks. On a clear fine day in perfect conditions, you'll maybe be able to stretch the RF to 2-5m, but that's only if there's no obstacles between the receiver and the transmitter. But the MX900 mouse is a bluetooth hub, which will work through thick walls (though I cannot really see the usage of that ability but..), let you connect up to 7 devices (including the mouse) through bluetooth to your computer (PDA, MobilePhone, headsets and so forth). But if you're just in for the mouse and not the bluetooth I'ld go for MX700. The 700 works nicely as a cordless mouse, and you'ld only have to charge it once a week, which is really no hassle. But if you don't require Cordless go for MX500, the smaller MX300 is a fav amongst the gaming society, though I find it too small.
Hmm looong reply..
Happy mousing
Hasse