This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
There are some efforts to write an operating system (almost) entirely in Java: JOS, JNode. None of those really took off as a serious operating system.
There have also been attempts at making CPUs that could directly execute Java bytecode as their native instruction set - see Java processor in Wikipedia for a few links. Those also haven't been very succesful.