I met Brian May, and he is an absolute gentleman. He's a very intelligent, charming man, a very deep thinker.
The Beverley Sisters sang at my wedding. My grandfather used to be their doctor, so my dad has known them for years.
I met Bobby Davro once - he was very nice and chatty.
Amy Winehouse, but not since she was a small girl. I used to teach her at Sunday School, and she was troubled even then, although she didn't wear her hair in a birds' nest, wasn't covered in tattoos and didn't have problems with substance abuse at the time...
My theory on whether 'celebs' are nice or not is that there are times when it's ok to go up to them and expect them to be all nice and charming, eg when they are 'on duty', and there are times when they should be left alone to be normal people, eg when they are out with their families or whatever. I'm sure there's nothing worse than being badgered by people asking for autographs when you're trying to have a meal with your husband/wife and kids. And yes, they are famous and in the public eye, but if they are famous for *something* rather than just famous for being famous or celebrities because they've been on Big Brother, then they should be afforded a certain amount of respect. A true musician/artist/scientist/whatever probably does what they do because it's what they have a passion for, not for the fame that comes with it. The ones that are snippy when cornered in public have a reason for being snippy.