I've spent so much time trying to connect my wireless mouse to my computer. I've Googled and searched user forums and tried all the fixes out there, to absolutely no avail.
Apparently there are a boatload of Mac users whose Bluetooth peripherals quit working after the most recent Lion OS upgrade. And there are lots of step-by-step solutions, beginning with turn the computer off and back on again, and going all the way up to reinstalling the OS.
I finally called Logitech Customer Support. The very nice young man (thank you, Chris!) first asked if I'd remembered to plug the USB receiver in.
Chris was sooooo gracious. Kudos to Logitech for hiring tech support people who have the good manners not to tell old ladies they probably shouldn't be playing with computers anyway. Heh.
To be fair to myself, I'd only used the wireless mouse a couple of times prior to upgrading my OS. Not having much familiarity with the device, I suppose I could be forgiven for forgetting about the tiny little receiver that makes the mouse work. Duh.