All the servers, personal computers AND super computers in the world COMBINED do not share enough computational power to put a dent in the Bitcoin network thanks to the widespread use of specialized Bitcoin mining hardware, i.e. ASIC Bitcoin miners.
This is missing the point. Bitcoin's value is completely derived from being able to convert it into tangible goods (well, basically cash at this point). They can easily make this conversion next to impossible for the majority of people. The fate of bitcoin rests completely in the hands of various governments, and I don't think its future is bright.
I would say it has stood the test of time for a few years now. Every attempt thus far (directly or otherwise) has strengthened it economically. The price is now around $250usd, doubled in the last month since silk road was closed down.
If the USA wanted to, it could easily destroy bitcoin, they have more than enough computing power.
It might not be legal for them to do so, but that's their own self imposed limitation, not inability.