I hate answering my phone in public and I almost never speak to someone on my cell phone in public. It just seems incredibly AWKWARD to talk to someone else about something private with a bunch of people around potentially listening (and yes- I do listen in on other people's phone conversations in public! )
I absolutley never answer my phone when out with other people because that's just plain rude.
Though, like evan, I also hide my monitor from others when typing online or even reading things online- I just don't like other people getting all up in my business
And I'm pretty damned extroverted as well...