Is the throw out bearing always spinning?
I guess yes because the spring between the bearing and the slave cylinder pushes the bearing against the fingers of the prassure plate which rotates with the engine.

I just wonder how this bearing can survive this continous rotation with just the original grease.

 

Yep always spinning, just under a load when pressure plate is disengaged.

 

Thanks! This was almost obvious... I was just looking at it and was thinkiong how is it possible. It's mounted on a piece of plastic and in front a thin metal sheet