Whenever I mention a real-world person (i.e., celebrity), product, or establishment that I find represented on Twitter, I'm going to @ it. More fun, though, is that some people on Twitter will show up (on first reference, at least) as characters in the novel. Some of them I know personally, and some of them I'm just picking because their profile pictures look interesting. Now, none of the people I'm going to use as characters actually know I'm going to use them, even the ones I know personally. That's probably because none of them know I'm even doing this project, though some of them will probably figure it out (as well as who I am) rather quickly.
I'd like to make it clear that, no matter who I end up using in this way, the characters are entirely fictional, and bear absolutely no relationship to the person I'm basing the character on. As I said, in a lot of cases, I just liked the profile picture.
See? It's fun living in the future, isn't it, kids?