I explained what the CentUp button is when I first uploaded it to Sketchy Details over the summer. Basically, it's a way for you, the reader, to support content you like directly. You upload money to your CentUp account and can drop in a few pennies here and there wherever you see participating sites you want to support. Simple as that. The CentUp team has really been working hard to improve and grow the service. They're running a promotion right now where you get 100 free credits to use however you want just for signing up. It's that simple. Just sign up and you have a free dollar you can break up however you want on sites participating in CentUp.
You might not think a couple pennies makes a difference, but it really does. Banner ads, video ads, sales on debut ebooks (ahem), and all the other monetization options available to a website rarely pay more than that on any given day. The difference here is you. Crowdsourcing is here to stay thanks to sites like Kickstarter and IndieGoGo. Musicians like Amanda Palmer and Radiohead are continually demonstrating the commercial viability of pay what you want releases of their content. All the CentUp participants are asking for is some spare change if you really enjoy what you're reading.