Just saw on the Adsense blog that there should be some new Referral buttons available. I think the buttons are still pretty ugly, but I do like the Firefox one. It's at least a step in the right direction!
There are exactly the same for me. Anyway I put them at the end of the page, since the AdSense buttons up to now were just outlines, reading the text from the button or from a text line is exactly the same, except at least the text has the same color as my other links.
I have never had very good results with referrals I think you have to have the right kind of site/blog to be successful with referrals, such as one about making money online.