Me and my better half are seeing some very similar issues with our iMac. The keyboard just randomly starts acting weird, I get the joy of repeated T's being entered, regardless of me pressing it or not. Its very inconsistant though, sometimes it just blocks and won't allow me to press anything. A reboot "fixes" the problem.
There's also problems with the mouse, suddenly it will start lagging very badly. This is far more frequent for me. So I had to change to a USB mouse.
Basically, it seems like bluetooth is pretty broken on OSX. I'm pretty surprised by this, the amount of little issues I've seen on our new iMac is quite worrying.