Guice injects constructors, fields and methods (any methods with any number of arguments, not just setters). Guice includes advanced features such as custom scopes, circular dependencies, static member injection, Spring integration, and AOP Alliance method interception, most of which you can ignore until you need it.
An earlier version of Guice already powers Struts 2's plugin architecture. Google has been running Guice in mission critical applications for months, and now you can, too. We hope you enjoy Guice as much as we do.