I started noticing changes on the YouTube header a few weeks ago! This just goes to show how little changes can make a big difference to conversions/sales!
Do small changes make a big difference? In the world of landing page testing, they certainly can. A few weeks ago, we ran one of the largest multivariate experiments ever: a 1,024 recipe experiment on 100% of our US-English homepage. Utilizing Google Website Optimizer, we made small changes to three sections on our homepage (see below), with the goal of increasing the number of people who signed up for an account. The results were impressive: the new page performed 15.7% better than the original, resulting in thousands more sign-ups and personalized views to the homepage every day.