This may seem a little simple but for me there are three factors in a popular blog.
The first being the content or subject of the blog. Being a twenty year old male I obviously don’t want to look at the hottest prom dresses of ’08 or Hilary Duffs new handbag. Although I’m sure there are people who are very interested in that, these blogs wouldn’t be of the highest interest to me. I would be more interested in a blog about sports, the outdoors, or Jessica Alba (for her great acting of course) and therefor be more likely to return to it. The more people that are interested in the content of a blog the better. The 2008 Presidential Election is appealing to most everyone in the United States. Because this subject is of interest to a greater mass of people than other topics, it’s popularity will be greater.
The second is the visual aspect of a blog. If it is appealing to my eyes I am more likely to stick around and check things out. Although the content of the prom dress blog above isn’t exactly what I want to read about, it is (in my opinion) visually appealing. This is a definite factor for me when I am digging through blogs.
The third is reliability of the content. I was searching through some WordPress blogs and found this blog. If I was going to buy a gaming system and was looking for some guidance, I wouldn’t want to spend $400 or so dollars on a system that someone says is better than another if he doesn’t even know anything about them. The creator of this blog seems to know what he’s talking about. I say this based on looking through other posts and such. He has a well set-up blog, with links of interest, solutions for problems, and is obviously dedicated to helping others with his knowledge.
These are the three factors I think contribute (in my personal case) to the popularity of a blog.