If you have the time, this video by Basho's CTO will give you a much better understanding of the tradeoffs that are involved in distributed system design: http://www.infoq.com/presentations/Concurrency-Scale-Distrib...

A great alternative to thinking about things in terms of CAP that Justin brings up is harvest-yield, where yield is the probability of completing a request and harvest is the fraction of your data that the response actually represents. Here's the paper: http://lab.mscs.mu.edu/Dist2012/lectures/HarvestYield.pdf