I have a Late 2011 27" iMac that once a day loses all bluetooth connectivity. (Very rarely it will drop just the keyboard or just the mouse, but 99% of the time, it's everything) This is a huge problem because I only have the iMac bluetooth keyboard and mouse, so this basically renders the entire computer useless.
The only solution I have so far is to hold down the power button to force the iMac to power down, and boot it up again. Everything works fine after booting it up, but I can guarantee sometime in the next 24 hours it will happen again.
Turning the mouse on/off, taking the batteries in/out and doing the same for the keyboard has no effect. The light on the bottom of the mouse blinks, but that's it.
It is not the battery levels; brand new batteries make no difference. On the rare occasion when it is just the keyboard that drops out, I can get it back by disabling it in the bluetooth menu and re-enabling it. Of course when the mouse drops out I've no idea how to use the keyboard-only to achieve the same actions.
Do I have a faulty iMac? I've only had it for less than 3 months, and although this did happen once or twice when I first got it, it was rock solid until the latest OS release that I upgraded to (Mountain Lion? I always forget those ridiculous names).