Before interviewing for a job, it’s reasonable and responsible to do some research on the people who are scheduled to interview you. This research might involve doing a few web searches to find out more about them, see what kinds of things they work on, maybe even learn about their interests so you can make small talk before the interview. That’s perfectly fine; they’ll be doing searches on you for the same reasons.
After waiting a reasonable amount of time following the interview (one to two weeks), it’s okay to email or call an interviewer or recruiter and ask for a status update. What’s not okay, though, is stalking an interviewer after the interview. Don’t send your interviewer friend requests on Facebook, Flickr, MySpace, Twitter, or any other social network. Don’t post comments on their personal blog mentioning the interview. LinkedIn is a grey area, but it’s probably best not to try to connect with your interviewer unless you’re offered a job (connecting with recruiters is probably okay).
Remember that your relationship with your interviewer is a business relationship, not a personal relationship, and it does not extend to blogs, social networks, and other non-work-related websites. Trying to wedge yourself into an interviewer’s personal life is rude and annoying, and it’s likely to give the interviewer a negative impression of your personality, even if you did well in the actual interviews.