Google Adsense Ads Scroller Feature? Why?

Last week I saw a couple of up/down arrows displayed next to the Google Adsense ads on my blog and, curious what it was, I clicked the down arrow - a bit worried that it might count as clicking on my own ads - but the ads simply changed. They changed five times to show different ads and then I could scroll back up through them again. How odd - what good is this to visitors? You know you are looking for a particular advertiser and want to find them? Maybe you are bored and just like studying others ad copy? Hmmm.

Anyway, the feature then disappeared for a week and I didn't see it again. So I kicked myself for not getting a screenshot and moved on. Today I saw it again, but so are others. Has this fully launched?

The first time this was spotted was apparently in December when a couple people on the Webmasterworld forums brought it up. Today there's a bit of buzz on it again.

My question is why?