I interview people for a living (I work in human resources/recruiting) I can tell you that a lof of companies, big and small, take way longer than necessary to make decisions and notify people of what's going to happen. It's horrible - sometimes I have people that hang on for a month before i can tell them they got the job or didn't get the job.

since it sounds like you've done all the right things - did a great interview and sent a Thank you - you kind of have to play the waiting game, which is definitely the hardest part. If the manager told you a certain amount of time, and that time passes, i think it's ok to make a quick call or send an email and let them know that you are still interested and just wanting to follow up on your interview. hopefully you will get a response after that, just so you have closure.
hope that helps and you get the job you want!