Cyrille Le Clerc & Nicolas Griso spoke yesterday about OSGi at the ParisJUG. We had a big picture of this specification: where does it came, history, governance, early adopters, future adoptions and expectations (french readers can consult this post).
The OSGi platform is a native competitor to JavaEE. Although, if you are not a middleware vendor, do not switch right now. It lacks productivity tools like annotations (due to old profiles compatibility: J2ME, J2SE1.1), testability is also immature (out-of-the platform testing is not provided, should reminds you old J2EE).
Keep it on your disruptive technology radar because it is really promising. In particular, have a look on the SpringDM (Dynamic Modules) initiative that adds the equivalent to the eclipse extension points. Then, you can declaratively add your business services (Spring beans) as OSGi-level services to contribute to the platform.