You can add this to the list of cool features about Google Search. There is a thread on SEW forums reporting that Google is dynamically placing content that is in the first sentence of a paragraph inside the title tag. For websites that contain the generic "index" that is often left in the title, Google has developed a way to instead of give you "index", it will find the most relevant piece of content and place it in the title.
One of the members reports that this might have been happened since last week. Barry sent me the Google Search that would return this result, instead of getting the sentence appear in the title tag, I got the following (thanks Shawn for the screenshot):
[See #5 where it says "index"] View image
Upon refreshing my browser I got search results (with an increase in ranking position - jumped from #5 to #4):
Now, I was trying to get back the original search that showed the "index" in the title, and found that if you modified the search you could get the results back if you knew originally what was in the title. See this search result. As you can see its back to being "index".
Pretty cool. If you are happening to see this as well, post a comment with the particular search.