As someone who once passed a bunch of tests (>40) to earn a bunch of Microsoft certifications(>20), I'm sometimes asked about the value of these certifications. Are they worth the time, cost and effort they take? What are the benefits? Who benefits most?

The real cost of certifications
More than the cost to sit the exam (typically $150) is the cost of studying for the exam. I used to spend weeks - at least a couple hours each day - studying for each exam. This cost tends to far outweigh the exam fee.

What do certifications prove?
A certification demonstrates a minimal level of competence in a given technology. They don't flag the holder as an expert; but, assuming you didn't cheat, they require knowledge of the subject matter in order to pass.

Everybody learns differently
I hope all of us can agree that it is not possible to succeed as a software developer, network engineer or database administrator without learning new skills every year. Each of us learns in a different way. I think most people learn a technology best when they have something to apply it to. This application serves as motivation to learn and retain knowledge. If your job doesn't provide that application, you need to create it yourself. This might be a personal or open source project or it might be a certification exam. Either way, if it helps you to learn a new skill by focusing on a tangible goal, that is a good thing.

When are certifications most valuable?
Certification is no substitute for experience, but it can help to supplement experience. This is especially true early in your career when practical experience is lacking. For those new to information technology or software development, it can be difficult to build up the experience necessary to impress a potential employer. A certification can help make up for a lack of experience, because you have demonstrated the ability to complete a goal and enough knowledge to pass an exam.

Some places require certification. Why?
Microsoft partners with companies in different ways. In some of these partnership arrangements, the partner company must have a certain percentage of their employees certified in Microsoft technology. Although far from perfect, it's a very simple way for Microsoft to vet their partners.

So is it worth it?
From a personal standpoint, I don't at all regret achieving the certifications that I did. I took most of the exams early in my career and they gained me some credibility. As recent as two years ago, potential employers asked me about my certification and were impressed when I provided it. I have learned a lot studying for these exams and that knowledge has helped my career. I doubt that I'll be taking many more exams. My free time is limited and I prefer to use more efficient ways to learn, focusing on building applications or preparing and delivering presentations.

My advice is to consider certifications early in your career to improve your skills and improve your credibility; then spend your time elsewhere as you solidify your credibility.