I've written a handful of them. None of them have ended up being big earners for me.
But, I do find them useful when I want to write a hub but I'm not 100% sure what I want to write about. I'll plug a few phrases into the hub title field and see what comes up. If a title sounds interesting, then I'm happy to write up a hub even if I'm not sure it'll earn a ton of money. I figure it's a gamble, and if I write enough I'll end up with some that get a decent amount of page views.