There are a lot of blogs out there and they fall into about three catagories. There are the professional for-profit sites like Wonkette and Defamer. These sites are self-supporting off of add revenue and the blogger's primary income is from the blog.
Then there are the serious hobbiest sites. I think most political blogs (which get all the press) fall into this category. Josh and Drink at Work and most webcomic sites also fall into this niche. They run ads and sell merch, but most of that has to be eaten up in overhead.
Then there are the novelty and vanity sites. I definitely find into this category. I have been on the "web" since the first Windows version of Prodigy. I've seen a lot of internet fads come and go.
Blogs and their related message forums are pretty much straight line descendants of local dial-up bulletin boards I was surfing in the mid '90's. These hobbiest boards had fiercely devoted memberships and often were strongly influenced by the personality of the board operator.
So with a dreadful signal to noise ratio in the blog world, what makes a blog popular? I think there are three elements: clever, crisp writing; relentlessly narrow focus; and frequent updating and posting.
People decry the loss of literacy the internet is mid-wifing, and you definitely could get that impression if you spent any time at all in an AOL chat room or browsing gaming forums. The good blogs though have a terse snarky style that makes paragons of tight writing like Entertainment Weekly or People look like Thomas Pynchon. If you can't get your point across in three paragraphs, you have lost the random surfer. And if you don't have something fresh to say, no one is going to bookmark you and come back.
This post is probably too long already by those standards. I will definitely come back to this topic. So bookmark this page and come back in a few days.