Are MVPs independent from Microsoft? How do they aid in the expanding and improving the use of Microsoft products?
Yes, MVPs are independent from Microsoft. To qualify as an MVP, one must actually not work directly for Microsoft, although many MVPs do work for Microsoft as an independent software vendor doing contractor work.
Externally to Microsoft MVPs act as industry experts and evangelists. We are given advanced access to (often NDA) early versions of Microsoft products and are expected to be well-versed in the use of those products well before the general public gets access. This in turn allows MVPs to write, speak, or answer questions about these products come release day. We also act as evangelists for Microsoft by blogging about our specific product expertise, talking about those at events, conducting seminars and training, and giving other such "real life" interaction with the community, especially with User Groups.
Internally MVPs also help Microsoft get their products to release quality. We are involved in early stages of product development with our respective Product Groups (a Product Group is a department inside Microsoft in charge of a specific product) and test, comment on, and many times critique products even before they get out to market. Many times we play the role of quality assurance for Microsoft and their products, and catch and notify them of many bugs way before Microsoft releases it to the general public. In fact we can be Microsoft's harshest critics -- and we're specially vocal when a bug or an issue has been pointed out way before release, left unfixed, and reaches the market!