A reality TV show is made by soliciting exhibitionists to improvise around a theme. They make their own humor and drama, and people watch. These websites are much the same: you come up with an idea--let's say, awkward family photos--publicize it, and watch the user submissions roll in. To make things easy on yourself, provide thumbs-up/thumbs-down buttons so your own readers can tell you what's funny. After a while, collect the highest rated ones and publish them as a book.
It's a business plan with a bottom line. Also: they're blogs.