blogged about Caffeine in Nov 2009, and it appears that google has been integrating the release of Caffeine (now Kaffein) gradually.
Starting on about April 1st, depending on your location on the planet, you may have seen some changes to your ranking.
Think your website speed doesn't matter? One of the new ranking factors with the rollout of Kaffein is speed. Kaffein incorporates a new speed ranking algorithm, and although google claims that this new factor only effects 1% or less of all search results, given that all other ranking factors are equal, your website speed will rank you above or below your competitors. Its a fact that bounce rates are higher amongst slower sites, and google factors this in as a less desirable search result. Cutts offers an explanation of speed based ranking and debunks a few misconceptions on his April 9 blog entry. "speeding up your website isn’t just something that can affect your search rankings–it’s a fantastic idea for your users".
Still don't think your site speed is that big of a deal? Lets talk about pay-per-click Ad-Words. I am getting reports from customers, that with the rollout of Kaffein, ad-words are costing more, and the additional cost is directly related to page speed. I have yet to verify this, but several marketing departments concur.
Google also seems to be ranking results and ads based on IP address geo-coding, meaning that relevancy now relates to your actual geographic location, or at least where google THINKS you are.
If you want to compare Kaffein results against the old google, check out http://www.comparecaffeine.com/ . Ranking differences seem to be fluctuating, indicating that google may still be tweaking the new algorithm.