I think there's an understandable negative attitude towards MS certifications amongst a lot of experienced developers. That's probably better than taking an overly rosy view of what certification can achieve, but I don't fully agree.

I've been using SQL Server professionally for about four years now, and took my MCTS in SQL 2008 development about a year ago. I'm currently preparing to take the latest entry-level C# exam in a couple of months' time. The value of these is definitely in giving structure and motivation to round out your knowledge in areas you might not otherwise have considered. If you're cheating at the exams, or doing the bare minimum of cramming to get a passing grade, don't bother!

That said, I don't plan to take a load more Microsoft exams after my next one. I think once you've got a good sense of the fundamentals, it's best to learn organically based upon what interests you and what you need on-the-job. I also suspect there are diminishing career returns unless you plan to really dig in and bet the farm on being a Microsoft specialist. My best guess is that improving my skills on something completely different (possibly Python, which I already know a bit of) will ultimately contribute more to making me a skilled developer than learning how to build Windows 8 Store apps, and ditto (e.g.) PostgreSQL or Neo4j on the database side of things.