[barik]

There are very few circumstances in which certifications are useful. Many companies will, however, pay for you to get certified as part of their employee benefit, so you should definitely take advantage of that. It will give you an opportunity to work on a new technology or develop a skill in an officially sanctioned way that can also be used during things like annual performance reviews.

Additionally, if you are any sort of consultant, having certification can help you acquire contracts.

Mainly, I've found certifications to be useful only when working with non-computer folks. Against your own peers they seem to have little to no weight. Fortunately, they don't really have any negative weight either, unless you go around flaunting them.