What constitutes an invasion of privacy?

I'm on the official John Barrowman mailing list and was disturbed by something I saw there.  Apparently, I could have read this wrong, someone saw John walking his dogs near his home and followed him home.  The person in question said she didn't stand there and snap pictures and that there were no signs that said keep out. From the tone of her post, it sounds like she's going to go back and stare in his backyard again unless he expressly says not to.  That's borderline stalker behavior.

Let me get this off my chest, and then you guys on my flist can tell me I'm wrong.  It's none of my business where a celebrity I like lives. If I happen to run into them on the street, or in a store, that's one thing. I've run into celebrities a few times when I worked at Barnes and Noble. I was always polite and professional knowing that they were there shopping and not there for me to drool over or harrass for an autograph. If I bumped into someone on the street or in a restauraunt, I would gauge the situation to see if it was an apporpirate time for asking for an autograph. 

At no time would I ever follow someone home and decide that now that I know where they live it's okay to keep going by their house whenever I feel like it.  Someone on the Barrowman list pointed out that John's partner Scott did not ask for people to start following him around just because the man he loves is famous. What if one of their nieces or nephews happened to be visiting? Just because Uncle John is a celebrity is no reason for their privacy to be invaded. And it is also an invasion of John's privacy.

Bottom line, public situations are one thing. If you want to ask someone for an autograph when you run into them on the street, at a store, in a restuaurant, whatever, that's your choice. Following them home is stepping across a fine line.