Many of the comments here seem to be unaware of what Stuxnet actually is or how it works. Symantec has a great whitepaper on it that is updated as they learn more. 50 pages of technical detail. Of course you can read the executive summary and at least avoid making the kinds of uniformed comments I'm seeing here.
Just a Few:
1. "People are so stupid to connect their industrial control system to the internet!"
Stuxnet does not require internet access. It delivers its payload in various ways, and in particular, if an infected USB stick is inserted into a susceptible machine, it will find a machine on that network with the Siemens PLC development environment and infect it in such a way to insert hidden malicious code into the PLC.
2. "Just don't run Windows"
There is some validity to this idea. But the payload was not delievered to a Windows machine, just via one. How many embedded controller development environments require a Windows machine? Try coding a Xilinx FPGA without a Windows box, or just about anything out there without one.
3. "We could have seen this coming"
Most people did see this coming. But they didn't think it was actually plausible to defend against. The Stuxnet worm required a huge amount of resources and detailed knowledge to pull off. Everything from the payload to the infection method. Someone really thought this through. It is a proof of concept of what people generally believed to be only possible in theory.
The fact that government is getting involved here is a bit worrisome. I hope they at least pay attention to the existing specifications already out there to help mitigate some of these threats. NIST 800-82 is a decent read that is free (final public draft) and there are other pay ones out there as well.
The reason why I am kindof annoyed about people's ignorance about Stuxnet is because the biggest lesson learned from it is largely being ignored. 1. That "air gap" protection you think you have is not as good as you think it is. 2. The "insider threat" is worth thinking about, even if you trust your insiders. They may not know they are a threat.