Hi,
It is very important to follow up. Call them and ask them if they have made any decision and tell them that you like their company and that you think the interview went really well. The best thing to do is to follow up right after the interview, leave a voice mail, send them a quick email but ALWAYS follow up. Sometimes they are not so quick in making their decision and to be honest if you are not selected I don't think they'll call you. So, pick up the phone
Good luck!