It has not yet occurred, Caffeine refers to their new algo update but I don't believe its showing in their "real" results yet.
It is very useful. Try to click on show options. There for example I go to look how many pages got indexed in what amount of time.
It's when you send a junior SEO worker out for more coffee Alternatively, click here: http://www.mattcutts.com/blog/caffeine-update/
Caffeine has been live for well over a month ( atleast that is what many people see) The test data center or sandbox data center if you will is exactly that, A place to test new algo's. Many think including myself any results you may be seeing there now may be testing grounds for the traditional holiday update that happen's around Thanksgiving.
You can take a look on this More info on the Caffeine Update Focus on the comments of some webmaster. Some are against with Google caffeine.