Interesting article from the BBC, apparently Google is showing older content to people using older versions of browsers.
On a Google forum its reported that users were encouraged to update their browser after a Google member of staff was quoted as saying its working as intended and that as they are continually making improvements to the search results, only limited support is provided for certain outdated browsers.
Safari 5.1 and Opera 12 seem to be the ones most affected by this move. Some of the support forum voiced they disapproval of this enforced upgrade saying that they like certain features of their current version of the browsers which are missing from current ones and went as far to say that they would now consider using Bing if things aren't resolved.
Full article is here - BBC News