I believe I have a similar problem. The magic mouse (and all other mouses) on my 2011 27" Imac (running 10.8.4) has/ve stopped working.
Initially the magic mouse was behaving erratically - jumping around, working intermitently, etc. I changed the batteries (now 100% charged, system preferences indicating paired and connected). That didn't help so I tried an SMC reset. That helped for about 5 minutes, and then problem resumed.
I then tried to switch to a usb conected mouse. Now even that mouse jumps to the top left corner each time I try to use it. This has rendered my imac virtually unusable. I am trying to edit a keynote document for an upcoming speech. I need to be able to use my mouse asap. (I am writing this note from my MacBook Air because my desktop is unusable). Any suggestions beyond the SMC reset (which failed to resolve the problem)?
In case it is relevant, this problem occurred *directly following* a Mountain Lion update this morning.
I don't mind using a USB cnnected mouse if I have to do so. Right now, however, even that is not working.