From the sounds of the latest Google video, Google is doing everything they can to help you get more traffic. This includes them helping to choose which is the best title and snippet to be shown in the search results. If Google thinks they have a better title for the pages on your website they are going to change it. They want to give readers the best description and title to describe what your site is about.
What do you think of Google changing titles and snippets for your website? Do you think this is helping to get more traffic to your site?