Google has changed appearance using Safari 5.1.1
I suspect it's an example of a new policy from Google, where they're deliberately showing old versions of their search pages if you use an out of date browser. You can find information about this from, for example, this BBC news report. 

It's probably a good idea to update Safari, for security reasons. This is what Google are trying to get you to do. But if you have a good reason to keep using 5.1.1, you can see an up-to-date Google homepage by changing the user agent string. There are instructions for doing this available online, e.g. here.