Has anyone tried ceramic bearings in a motor? Does it work?

It goes if you can maximize it. Im sure its hardly noticeable but the motor will have less friction and rev a bit quicker and higher.

So this would help a 4x4 motor run cooler? Like a 4x4 buggy that always needs help.

I'd say the effect on cooling is probably negligible. Ceramic bearing have just a little less friction than standard bearings, but are also more fragile. Anyway, the effects aren't that big all around. It's just that little last half of one percent or so... most people (incl. me) lose more time each lap with our (slightly) inconsistent driving than they could ever gain with these bearings during the whole race.