The Wikimedia foundation is currently working on a new skin for Wikipedia and other Wikimedia sites named Vector. It will replace the current skin known as Monobook. In short the Usability Initaitve is a small group funded by the Wikimedia Foundation to design, prototype and user test a new interface for MediaWiki (The software for the wiki). I personally find the new interface very modern, and welcoming. Here's a screenshot of the skin on wikipedia.
Hey mister, I want to try this
Cool. You'll need to sign up for an account at Wikipedia, which you can do by clicking here. After you've got your account sorted and are logged in, go to the Opt-in page to switch to the new theme. Good luck.
I want to help out with the project
Head over to the usability wiki and look around on the prototype talk page and let them know what you think. You might also want to help out with the browser compatibility checking.