Bluetooth Keyboard Lag
While it doesn't happen all the time, it IS a problem. My first solution was to turn Bluetooth off on my iMac, but as you can guess, then I have no devices to turn it back on again. I have a wired mouse close by that I've been using for this, but someone suggested just turning off the keyboard, and then back on, so I'll give that a try next time this happens. This is why I'm not a fan of wireless input devices.
And the funny thing is, when the keyboard is in Lag Mode, the wireless mouse works just fine. Go Figure.