As far as I understand, the service provided will be a respository of badges. Your site will have to determine what the badges are and when to award them to users. Then you'll let Webchiever know about it so they can store a copy. This way users have one place to show off all their badges.

In regards to how difficult it is. The repository concept itself isn't hard, but the idea is if you can get enough sites to use you then I imagine other sites will see the site as a great advertising opportunity and will want to award badges just to get visibility on the site.

The rule engine is a different story. (Of course I'm very bias) A 3rd party rule engine is useful if you plan to constantly add badges and/or change the conditions which award a badge. Otherwise you need a developer to essentially rewrite your badge awarding queries or code every time you want to make a change. Or write your own flexible rule engine with a management UI. :)