Via Doc Searls, I found this piece by Hugh Macleod. I liked a lot of what he said, and this in particular makes some sense:

That's easy enough to explain. Blogging is all about ECO-logy. Branding is all about EGO-logy. The two are not compatible. Which is why brand-wimpy Microsoft has hundreds of bloggers [a well-known fact], and why you can get fired for blogging at uber-brand Apple [so I've been told].

Certainly true of his examples, and of a few other places that come to mind :) However, I don't go with him on his "branding is dead" theory. I think Apple's entire iPod campaign pretty much puts the lie to that. If you have a compelling product, a good branding/marketing campaign still works. But it has to be a good product - it's really, really hard to promote crap with all the word of mouth that spreads over the net.