In this blog on reddit, the developers of IBM's Watson mentioned that the code was mostly written in Java, with significant chunks written in C++ and Prolog, running on Linux. Here's an excerpt:

"Watson is powered by 10 racks of IBM Power 750 servers running Linux, and uses 15 terabytes of RAM, 2,880 processor cores and is capable of operating at 80 teraflops. Watson was written in mostly Java but also significant chunks of code are written C++ and Prolog, all components are deployed and integrated using UIMA."

While, in a way, this impressive feat is a testament to IBM's Power architecture and its ability to easily perform parallel tasks, I'm mostly sold on the RAM. 15 terabytes of RAM? That's a huge enabler! I predict that, based on the success of solid state disks and the common sense performance boost RAM gives you, we'll begin to see computers with battery-backed RAM disks in the future. And it's really nice to see Java is still at the center of ground-breaking achievements such as this, which is a good indicator of the future of computing. Take note, all of you out there proclaiming Java's decline!

Happy coding!
-EJB