I have several friends on Examiner.com but had not really thought about signing up until recently. They do not give up-front payments, but they do give revenue share. They do not tell you exactly how much, just that it's based on a variety of factors. When you sign up, you have to submit a writing sample and explain why you are a good fit for the position, just like applying for a job...and you may or may not be selected. If you are, they perform a brief and simple background check on you (mostly, where you've lived recently and if you have any convictions).
I signed up and was accepted as the Sacramento Equestrian Examiner last week. It took them just under a week to send my acceptance, but I've heard of other people taking longer or shorter so it probably depends on the channel you choose. They expect you to post 3-5 articles per week so you can build a readership, but I have not found any guidelines that say how long the article has to be. They do want a picture with every article, as well as hyperlinks within it to relevant websites. It's kind of a pain, but if I'm honest about it, those things probably do enhance the article and make it more appealing. The channel managers are very good about providing helpful information to make your article appear professional and draw traffic.
I have only posted two articles so far, and one of them was late last night. Sacramento Equestrian is probably not the most popular subject to search for, so I'm thinking of getting something more mainstream as a second topic(will post on that later if I do). I have about 30 views so far and $.27, so about a penny a view. Like any content site, this is not a place to get rich, nor should anyone quit their day job to work for Examiner.com. however, it'll be a little side income, and they do not ask for exclusivity on anything you publish there.
The thing that really prompted me to sign up was that a lot of people have gotten some good connections through their Examiner.com articles...invitations to events, requests for reviews, etc. I haven't heard nearly as many stories of this type from other online content sites. I also like that Examiner.com is somewhat exclusive--unlike Associated Content or Helium, where anyone can write anything, Examiner.com, like Suite101, has standards. Like my blatant self-promotion there? :)
I'll report back in a couple of months when I have a good base of articles going.