What's that ball doing in your can of Guinness? Well, Tory of Hobson's Choice blog found out the answer:
Basically, the small plastic ball is called a widget. The purpose of the widget is to release CO2 from some of the beer in the can to create the head. It is meant to mimic the texture and head of Guinness on tap.
Mystery solved! http://www.toryhobson.com/new/entries/not-your-macs-widget/ | Longer explanation at How Stuff Works - Thanks Tory!
For the more curious, it'sexplained pretty well at
http://en.wikipedia.org/wiki/Widget_%28beer%29
And, yes, it is nitrogen, not carbon dioxide which is added.
The cans and bottles still don't compare to the draft form.
"When you open the can, the pressure inside immediately drops, the compressed gas inside the sphere quickly forces the beer out through the tiny hole into the can. As the beer rushes through the tiny hole, this agitation causes the CO2 that is dissolved in the beer to form tiny bubbles that rise to the surface of the beer. These bubbles help form the head."
Ingenious, really. Though I prefer Ramune's visuals and neato bottle design.
How do they recycle them?