I've just noticed that you get a different choice of referral buttons depending on your choice of language, specifically US English and UK English. For example, Firefox in US English has buttons for "more secure browsing", while UK English has buttons for "faster browsing" and "better browsing". The same is true of Picasa - I haven't looked at the other two products. So, I'm now showing a (random) mixture of buttons from both languages across my site, in a variety of colours to combat ad blindness. What would be really good is for Google to display the referral buttons in the appropriate language for the user. My site is accessed worldwide, and a significant portion of traffic comes from non-english speaking countries. I could probably code something up myself to do this, but I don't think it's worth it. Cryo.