It's tricky, right? We blog a lot for a company our size --- multiple books worth of technical writing on the blog --- and we still feel like we have to be ultra-careful about promoting ourselves to keep people from feeling like we're just trying to sell something. For instance, I'm not sure we've ever worked in a call to action for our consulting services in a post.
It's definitely one of the things I'm most impressed about with 37s and Fog Creek, that they've managed to extract so much business value out of their blogs.
Reading Spolsky back in '03-'04 was what made me want to become a product manager, which I was pretty quickly able to do, which experience taught me what little I know now about the software business (you know, besides actually writing and shipping code, and, uh, getting funding, neither of which appear to have any correlation with success in the business ;] ).
I actually think Spolsky's weakest on the hard tech content, and strongest on the product marketing side.