A single GPU supercomputers worth some millions of $ would have more power than the bitcoin network.
The top 500 contains multiple supercomputers which use GPUs. The #2 supercomputer (which was the #1 not so long ago) gets roughly 30% of its computational power from over 7600 NVidia GPUs. The reality is just that supercomputer are ill suited for mining. They are inefficient on a MH/$ and MH/W basis because they tend to have lots of expensive (and power guzzling) stuff which do nothing for Bitcoin Mining. Components like massive memory banks (as in hundreds of TBs), redundant high speed storage arrays (think thousands of 15K RPM SAS drives and now SSDs), ultra low latency high speed interconnects (20Gbps fiberchannel), node redundancy, etc.
Sure you could use a Supercomputer for bitcoin mining, and you could also use a ferrari for hauling gravel. Doesn't mean it is a good fit.
first i want to say that i agree with you, and that you are one of my favorite posters...
that said, i LOVE how no matter what the discussion is it comes back to MH/$ and MH/W
the other thing that i think we need to consider here is that there is very little need for the government to do this.. in the grand scheme of things even if they comprehend what bitcoins are.. they are such a low priority threat..