If Google SERP Experiments, Caught in the Wild

It’s 5/6/2011, a Friday night at 10 pm on the East coast. Google constantly experiments with the SERP page to increase its performance metrics, and tonight I seem to have stumbled on to one.

Look at the two examples below taken just 10 minutes apart from each other. What I’m assuming is the test one on the left has a cleaner look, with lots more space around the results. Interestingly there seems to be only one site less on the page for all this extra space.

Take a look at the example screen shots below comparing Google’s SERP results. Event though the search query is not identical the SERP pages are very different. On the left there is a significant space between the top Paid and Organic results, while the space between the right gutter paid results remains the same. They also seem to be playing with the font color, and they removed the cached and similar links.

Take a look.

What do you think? What other changes have you seen Google test recently?

More importantly, how often do you test your site to see if it is performing at its peak potential?