The results reported by danudey should not come as a surprise. The EC2 micro instances are designed for situations where short bursts of CPU are the norm. They were not intended to be used for continuous, compute-intensive chores.
I think the reason I was 'surprised' is that I expected the 'good for sudden bursts of CPU' to be what it was good for, rather than an actual hard limitation on how it works. Perhaps this is because I'm not terribly familiar with how EC2 is managed behind the scenes, being a new convert from Rackspace.
My post was mostly meant to illustrate that Amazon puts hard limits on how your VM operates (which makes it inconsistent over time under load), vs. Rackspace, which gives you a constant amount of CPU capacity all the time.
