I have got MCSD status now, and passed all 4 exams for the first time.

I think there are two main reasons to get certified.
The first reason is, like Lethal already said, industry recognition. It looks good on your resumee.
The second reason is, and I found it out after I started, was that you got a wider knowlegde about Vb (assuming you do the VB exams). Before I started studying, I had knowlegde about the things I needed to know, and about the things I liked to know. Now i have a good insight in the whole package, and if I might need it, I know where to find it.

A good test to know if your prepared well enough, is taking a transcender exam (www.transcender.com). I know they are expensive, but it are the only test exams that are similar to the real ones. If you pass the transcender exams, you most likely pass the real ones too.

I studied for it by taking instructor ledd classes (the company paid).
But in addition to these (and the Microsoft study material that came with it) I used the New Riders books (www.newriders.com). They are pretty good. Just don't rely on the test exams that come with the books, only the transcender exams are like the real ones.

Good luck