Here you can view all significant Google updates ever made: http://www.seomoz.org/google-algorithm-change#view-all So the last one was on January 22 and it was Panda update.
I think in this day and age focusing on other avenues of traffic is key, as Google is completely unreliable and have shown they have no issue with wiping out small business sites left and right. Worrying about the next Google update is too stressful.
Each day Google updates its way of working, but if i talk about the recent update of Google, then its Panda 24, and in this update Google has explained about the content quality of a website, means those websites which provides qaulity content to their users, can only rank well. If you wan to know the main updates of Google, then read about Google penguin and panda updates till now.
Google Panda is a change to Google's search results ranking algorithm that was first released in February 2011. The change aimed to lower the rank of "low-quality sites" or "thin sites", and return higher-quality sites near the top of the search results. CNET reported a surge in the rankings of news websites and social networking sites, and a drop in rankings for sites containing large amounts of advertising.