You are not alone my friend - I have this problem too
Since 'upgrading' to OSX 10.8.2 my Magic Trackpad is 'magically' clicking and right-clicking stuff all by itself...
Only happened since 10.8.2 so nothing to do with the hardware.
Having to use internal trackpad on my rMBP now as Magic Trackpad is unusable until this bug is fixed
Hopefully, we won't have to wait too long for Apple to identify the cause and get a fix out...