No one has mentioned the particular case of consulting/contracting. If you are in this category or you would like to be, this can definitely help you.
You are easier to 'sell' on a project if your boss or sales guy can pitch you as being certified in 'niche category X'.
That being said you are not necessarily better or more knowledgeable on a particular topic if you are not certified, and I agree with others who might take a dubious take on them in general. Although, having a few MS certifications I can say for you, if you crank on them on a technology that you are trying to learn, it really forces you to get up to speed.