And of course, you can always just post into the threads already going out there in the Community Forums such as this one.
If you want to write a letter or call
Corporate Headquarters
Address
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Telephone
1-800-MICROSOFT ([removed])
Fax
Please include the recipient's first and last name.
1-425-93-MSFAX ([removed])