Have loved my Magic Trackpad since it first came out. Since upgrading to Mountain Lion, the system fails to recognize the Trackpad after a reboot. I need to pull the batteries, reload them, and power the Trackpad on... then the Mac sees it. But even then, it won't accept any clicks, it just moves the cursor around. I also tried an old fashioned USB mouse... it needs to be unplugged and plugged back in, but like the Trackpad, that allows cursor movement, but it also won't accept clicks (which makes me believe it is not a Trackpad problem). The machine is a MacPro 3,1 dual quad-core (2008).
My workaround in the meantime is (I think) going to be to remove my wife's user account, then I don't need to click to choose the user. But it is extremely annoying.
Anyone else come across this and have a fix?