He left me alone in his place for the first time

Agree with both gents so far.. It is definitely a good sign. He likes you, he knows you, and trusts you... he is comfortable enough with you that he can leave you alone at his place..

Be careful though, one of my friends always used to do this to the girls he thought he would go out with to see what they would do. And he had cameras installed all around so that he could watch her later on and see what she got herself into when left alone in the house.

It was amazing with this one girl who went thru almost everything and I mean everything in the house, as if she was looking for something :) He obviously wasn't happy about it and never called her back or answered her calls. I don't think she knows the reason why she got dumped to this day.

Well it's certainly not a bad sign. I wouldn't blow it out of proportion, but it sounds like things are going well.

I only do that with a girl that I like, and trust. So in a way it could be a big deal cause yea, if I didn't trust the girl and liked her that much, I would never leaver her home alone unsupervised.