UML is gaining increased attention as a system design language, as indicated by current standardization activities such as the SysML initiative and the UML for SoC Forum. Moreover the adoption of UML 2 is a significant step towards a broader range of modeling capabilities. This paper provides an overview of the impact of these recent advances on the application of UML for SoC and NoC development, proposes a modeldriven development method taking benefit of the best techniques recently introduced, and investigates the design of power efficient systems with UML.