I just got the Logitech Anywhere Mouse MX and I love it. I was initially opposed to having a receiver and really wanted Bluetooth, but the disadvantages of Bluetooth mouses really outweigh their advantages.
I haven't really noticed any major disadvantages by having a Bluetooth mouse. I now have:
One extra USB port free (I have a LOT of USB devices hooked up, and I still need to unplug every once in awhile...)
No noticeable lag vs. the Logitech MX Revolution USB mouse I was using previously
No lag on my Bluetooth KEYBOARD -- my Cordless Wave Pro had major issues where sometimes I had to move my hand to the right edge of the keyboard for the text to appear.
Even though my new keyboard isn't supported on the Mac by Logitech, the Option-Eject works to eject my 2nd DVD drive. My Cordless Wave pro would only eject the first DVD whether I did Eject or Option-Eject...and that keyboard WAS supported for Mac!
Easy recharge stand for the mouse, which can easily go 2-3 weeks without needing a charge.
The *ONLY* issue I have is if I accidentally hit the "connect" button on the bottom of the keyboard or mouse (pretty rare, cos it's hard to "accidentally" hit)...then it says it's detecting it, but never finds it. I have to go back and set up a new Bluetooth device and delete the original.
Your experience may be different, but I have ZERO reservations about using Bluetooth over USB (and if your USB dongle gets lost or damaged, I don't think you can just use any USB dongle...I may be wrong about that though.)