I know 4 people who have obtained MBAs in the past 5 or 6 years. Currently, none of them have advanced in their careers and in fact, a couple have been demoted -- and this was in a company and department that valued the MBA. Fortunately for those two, the company paid 100% of the cost of the degree so their only investment was time.
Personally, I find it of questionable value but even still, I have considered it but just can't make the committment right now. If you have the opportunity for your employer to pay for it, do it. It can't hurt.