Have only really met a few celebs although I've seen or said hello to quite a lot more. Most were perfectly friendly but the ones that stick out as being really great are:
Mark Wingett (DC Carver in the Bill) who was fantastic and made me feel that I was the most important person in the world.
Graham Murty (Reading FC captain) who helped coach my daughter's football team when he was only supposed to be presenting an award at the end of the match.
Andrew Marr - very funny and clever man.
Lynda Bellingham and Julia Hills (2.4 children) were lovely when I met them after a show they did recently.
The lad who plays Seamus in Harry Potter was really sweet to my 11 year old daughter and waited patiently while I took a photo of the two of them.
My OH said Anton Rodgers used to regularly pop in for a chat where he works and when he (Rodgers not my OH) died everyone was genuinely upset as he was such a great guy.
But for me the best one was the late Diana Dors who was wonderful and would often take me shopping as she didn't have a daughter to shop with!!