Some new stats have been added to all user accounts on the site called "Activity Points" or AP.
Each time you perform a beneficial action on a Nexus site you'll gain AP so that other users of the site can see how much you have done on the Nexus sites. The more AP you accrue the higher your level and rank on the sites will be. At the moment AP and levels are just for show; they don't unlock any special features or secret sections of the site but who knows, maybe in the future your AP might be put to good use.
For more information on Action Points including what actions will increase your action points and by how much check out the article I've written
on action points.
Your action points are shown in your profile (with a break-down of what actions have given you points) as well as when you post on the forums or leave comments on files, images and articles.