I'm not sure what would constitute spying either but, during the time I had a Facebook account (I didn't stick around too long - it was too, well let's just say it wasn't for me) I remember somebody saying (about one of our mutual friends) 'You should look for his pictures. He has some pictures on his Facebook account'. I just felt really creepy about that. I guess I'm just not very nosey.
It's probably been 2-3 years since I left Facebook and I've never had any desire to go back. I'm not dogging others for using it, of course. It just wasn't for me.