"The new, larger Google search box features larger text when you type so you can see your query more clearly. It also uses a larger text size for the suggestions below the search box, making it easier to select one of the possible refinements. (...) Google has always been first and foremost about search, and we're committed to building and powering the best search on the web — now available through a supersized search box."
If you don't see the redesigned homepage, then the data center you hit hasn't updated it. For those that are curious, Google uses a 17-pixel font for the search box, up from 13 pixels.
Update: You can go back to the old interface using a Greasemonkey script.