Not a nonsense question at all - actually a very good question!
Acropolis had some similarities to Unity in as much as it tried to provide support for the Dependency Injection (or Inversion Of Control) pattern which helps you connect pluggable components together through composition without having to write a lot of hard-to-maintain code. Acropolis was specifically targeted at composite client applications and we used this pattern to help manage the parts, views, and services within the application and to connect them together in a simple but flexible and configurable way.
Unfortunately, the Acropolis project was halted before we were able to release strong support for the DI/IoC pattern within Acropolis itself. So in the CTP releases the pattern was never available to the developer as an extensible part of the framework.
Unity, on the other hand, is an application block that was specifically created to support the DI/IoC pattern. You can use Unity in a variety of apps, not just composite client applications (though that is where it was originally targeted) and it will continue to evolve via the community and be integrated into other Patterns and Practices application blocks. In particular the upcoming Prism project (which will provide support for WPF composite client apps) will allow Unity to be fully utilized.
So in short, if you need support for the DI/IoC pattern in your application, Unity is well worth checking out.
Hope this helps.
David.
