He's in his cave about 20% of the time, he's really active. He only hides in the cave when i make a sudden move, he sulks a bit then comes out claws waving trying to get revenge! He also tries to take chunks out of my fingers when i do a water change, or even if i just put them up to to the tank wall! He patrols the tank and redecorates it on a regular basis, so it always looks a scrow. It'll never be a tidy tank with Thermi in it, but he's cool enought to justify a scruffy tank.
I do have a couple of issues with him though, as the tank is in my bedroom he seems to think it is great fun to lean up against the side of the tank and bang his claws on the glass through the night. Most annoying when you are trying to sleep! Also i have to put a cloth over the tank whenever my GF comes round, as she is scared of him!