What Makes an Effective Blog?

What makes a blog effective? I've been looking at good blogs in an effort to answer this question, and I've noticed that the blogs I admire tend to have certain characteristics in common.

• Focus The best blogs have a well defined focus (unlike this one), which they stick to. Look at Beyond Bullets. It's about one thing: better PowerPoint. Now maybe you don't care about giving better PowerPoint. In that case, you're not a potential consumer of this blog.
  
• Content Just having a blog isn't enough to make it interesting. Links to other sites are nice, but not enough to make a blog compelling. You need to include valueable content for your readers. Look at Koly Parnell's tech blog. All the content is useful. Some of it is technical content of use to developers. He also includes personal observations and insights gleaned from his experience in the development world. It's the latter that really puts this blog over the top. Technical information is nice, but experience is gold.
  
• Conversation Your blog isn't your private podium from which to hold forth. It's a conversation. Not only does this mean you should respond to comments, but that you should highlight good comments in your posts, even if they are critical of you. People may visit for content, but they'll return for conversation. Hugh MacLeod, among others, does this very well.
  
• Truth This one's last in the list, but first in importance. I don't mean you should slag your friends and slam your employer, rather that you should strive tobe truthful (if tactful) at all times. Scobel is the king of this. That's how he came to be recognized as an extremely credible source while working for the software company that people love to hate. He doesn't hesitate to praise Microsoft's competition when it's deserved, or to criticise his company when they deserve it.
  

That's not an exhaustive list, nor do all the points apply to every blog. My blog violates point one all the time. That's fine though, because this blog's about my interests and is targetted at my friends who share those interests. You can bet that when I publish a book, it'll have it's own blog, because that's the right way to promote a book.

I want to emphasize that these opinions are based on observation of the blogs that I admire most. You can probably (maybe) find great blogs that break these rules, but if you do, I'd like to know.