On my AOL journal, I listed various reasons why I choose to read certain blogs.
I'll use this spot to discuss reasons I will not read some.
The number one thing I dislike, and something I never encountered on AOL journals: blogs that advertise things, with no personal content whatsoever. Why would anyone return to read such junk? I have advertising forced upon me from TV, billboards, and yes, the Internet. But I won't choose to spend time on a blog full of advertising. More power to you if you make money from pay-per-post. It just isn't my cup of tea.
Now, I have found some blogs of interest that include ads on the sidebar; I wish they didn't, but if the content of the entries holds my interest, I will return. As long as there aren't too many ads.
Another thing I don't care for, although I will put up with it in a journal I otherwise like, is a bunch of artificial graphics. You know, cartoon-y figures of witches or angels or vamps holding whips, or homey little "artistic portrayals" of cottages and such. I love photographs. I despise fake-looking pictures of sirens and mermaids that don't even vaguely resemble the author of the blog.
But that's just me.