Mainly I write about web design. Of course, to me, web design is incredibly personal. It's an ironic title but some people may miss that. Two things, really. The first is that web design is communication.
Good websites are conversations.
The second thing all web designers should know is that the way we build sites must change and will. Suffice to say, the Web is broken, and all of us helped to break it. All of us can fix that by learning about and using W3C recommendations, but at a cost of decreased attractiveness and limited functionality in browsers, which don't support these recommendations. For more about that, read To Hell with Bad Browsers at A List Apart. Pardon the plug.