It's new logo day at Google, and that means your favorite apps are getting a few icon tweaks. Several of Google's apps had the little 'g' somewhere, but that's no longer part of the logo. Now it's all about the big G, and Google is already updating icons on the web to reflect that.
The Google+ icon and main search icons are the most drastic changes. They were basically just the lower case g before, so now they're just the upper case sans-serif G. The rest of them have the new G swapped in for the old one.
These icons are only on the web so far, but you can bet the Android apps will get new icons soon as well. Maybe even on update Wednesday tomorrow.