Unity is the name of the new container in Enterprise Library 4, built on ObjectBuilder 2. The P&P team is holding a free 2-day workshop on the extensibility of the Unity container. My current project will be keeping me too busy to be able to go, unfortunately.
We did get a look at the Unity container at Seattle Code Camp last weekend (thanks to Chris Tavares who stepped in at the last minute to offer us all the sneak peek). It's like a very well fleshed out version of the ExtensibleContainer sample, and I'm excited for release so I get to use it, too. :)