The more you try to control the message, the less effective the message will be. The reason is that people today can tell the difference between valuable information and canned marketing material.
Picked this up via a post in Richard Gayle's blog. I wish all companies were so open to giving up some control (hint, hint). That reinforces a good article ("A Better Longhorn Through Blogging") on how Microsoft bloggers are opening up Microsoft's development process and making it more transparent by writing about it as they do it.