I met Bill Nye in person once when I was a teenager. My mom got a ticket to a showing of Bill Nye: Science Guy, the documentary about him, when the film first came out, and he was there in person for the showing and a Q and A afterwards. He was really sweet and funny in person, with an appreciable sarcastic side. He's also taller than I had imagined in person.
I've also seen multiple Star Trek actors at convention panels I attended in person, and I've asked questions directly to Johnathan Frakes and Brent Spiner at their Q and A segments.