There's a fine line in how you follow-up after an interview. I've interviewed candidates and then never heard from them again. I've also had candidates who called me literally every day, left me messages constantly and tried to fake out my assistant in order to get through to me. These are candidates I WOULD have hired...but then they sort of creeped me out. So here's some general rules:
1. Send a thank you email after your interview. Send it to everyone who interviewed you (ask for everyone's card at the end of your interview so you have the contact information). Reiterate why you are interested in the position based on what you learned through the interview.
2. Send a hand-written thank you note as well for extra bonus points.
3. If you don't hear back after one week, call or send an email to inquire about the next steps.
4. Then stop. If you haven't heard back after that, you didn't get the job and will likely receive a letter or email soon to inform you. If you are still in the running, the hiring manager won't keep you in the dark.
ONE EXCEPTION: If you have a competing offer on the table, let the hiring manager know ASAP. This is crucial information for me. It often takes about a week for me to get approval for hiring from my VPs and knowing that we could lose you usually gets me approval within a couple hours.
In short, follow up with me afterwards but don't become a stalker.