There's probably few people who haven't over celebrated a milestone. I certainly have. It is just nature for us to acknowledge an achievement that came with a lot of hardwork and dedication, at least in most cases. When things come together after a whole lot of effort it certainly calls for some form of acknowledgement.
Yet we often replace acknowledgement with full blown celebration for a destination that we haven't yet attained. The easiest example I can give is the few times I have been promoted at the office. There's always a sense of gratitude and appreciation yet am even more conscious of the work and hat lays ahead. It is more a less a call to real and difficult justification of whatever acknowledgement we have received.
The goal is to not get carried away that's all. It sounds a lot simpler than it actually is. There's also the case of how soon one should move on to justification after the achievement. I usually celebrate for a day or two before moving on. I certainly don't think anything more than a week of celebration helps the purpose.
The extreme of course is those odd cases of Workaholics who don't take any time to acknowledge their feats. I don't want to be part of such a group either. Every effort that yields results needs to be acknowledged and celebrated, but we must be careful to remember that work lies ahead.