As noted over on the Partner Success Blog, The new Force.com AppExchange is now LIVE!. The post points out several features that are new, and also points to an interesting webinar that illustrates many of the features.
For those new to AppExchange, this is how I described Force.com AppExchange last year: A user of your packaged application will be a user of the Force.com platform, so it makes sense for there to be a central directory of applications, making it easy to share, find and install applications with the rest of the salesforce.com community building on the platform. Enter Force.com AppExchange. It’s an on-demand application directory service from that allows you to browse, install, and share apps and components built for the Force.com platform.
You can try AppExchange for yourself here.