There are very few ways to quickly prove to yourself that you really have touched the breadth of knowledge in a specific area. Certification are a way to not only guide you through the roots of emerging technologies, they offer you a way to measure your understanding of these new technologies.
Microsoft offers two categories of exams; Those that are technical based (such as 70-487) and those that are Job-Role based (such as 70-583).
A technical based exam focuses on “How” to do stuff with a technology whereas a job-rolebased exam focuses on “Why, when and where” to do stuff with technology.
e.g. A technical based exam might ask “How to implement (code) IDisposable interface in a class?” whereas a job-role based exam might ask “Why and when you should implement the IDisposable interface”.
Whether you should do exam 70-583 or 70-487 really depends on whether you want to be a developer or a designer. If you’ve 3yrs experience as a developer, you should probably do 70-487 (and then maybe do 70-583 as I don’t believe you can be a developer without knowing how to design – IMOA).