Great article by Greg Arnette about the crashing cost of CPU Costs over the years, thanks to the introduction of the cloud.
http://www.gregarnette.com/blog/2011/11/a-brief-history-cloud-cpu-costs-over-the-past-5-years/
Personally, I think the most profound one was in December 2009 with the introduction of “spot pricing”.
Effectively you have an auction for the cost of an instance at any time and so long as the prevailing price is lower than the price you are willing to pay, you get to keep your instance.
Hype Cycles 