I say a blog is about the democratisation of information and a facility to share and exchange views and information. Scott Savage, the Microsoft Student Partner from University of Sydney wrote an entry about the meaning and purpose of blogging "The Importance of Community" on TechTalk Blogs. He raised the importance of this medium to engage with the readers and have a real conversation. Technology marketers' blogs who just flogged/ regurgitated the company lines buy no mileage with the technical community.
Cos we can see thru their smoke screen!