Seen these ScratchBack widgets popping up lately so I thought I'd give it a try, the widget is just to your right, I don't expect to get any tips, but I'll leave it up as an example.
If you have a paypal account, buying a place in "Get In My Top Spots" is easy as, click it sign into paypal, pay and your all done, your link should appear in the widget.
I've tipped a couple sites and the process was really easy, though the selection of sites to choose from at the moment isn't the best, but I'm guessing that once the user base increases the market will become pretty competitive. It also seems to me that most people are opting for the autobump option, where your link slides down the widget and eventually gets bumped off the list. They also have daily, weekly and monthly options available and you can set you own prices, I've set my widget up for $5 for a month.
Other than that I don't know to much else about the service, seems like an interesting idea though.