Part of how he raised $40M is by writing good blog posts ;)
While Ning is a great platform, and a lot of his success is attributable to earlier success (Netscape/etc), an important part of the whole process is having people know your stuff, know you're thinking intelligently, and be impressed with you.
VC's are human too. If they're reading your blog posts and finding genuine insight, hearing about your material on the radio, and like you, that'll play a factor in valuation. [1]
-Colin
[1] I don't have a source for this handy, but I've read several VCs talking about this process. Basically, it comes down to being Noteworthy. See: Seth Godin.