Starting yesterday, many Google AdWords advertisers began noticing a message in the AdWords console asking them to give the new user interface a try. Google began beta testing the new AdWords UI in November 2008 and expanded the beta in March 2009. More recently, they asked advertisers to experiment with the new UI early because it will be here soon.
Well, now it is here and most advertisers can switch over to it. When you login to your AdWords account, you should see a bubble notification that looks like this:
Note, when I upgraded, I was told my browser (Safari 3.2) may not be fully supported and I should use Internet Explorer 7, Firefox 3, or Chrome to manage my campaigns. In any event, you likely can upgrade but before doing so, if you want to learn more about the UI, see this resource for more information.
Forum discussion at WebmasterWorld.