The attached pdf file contains a paper written by Professor Wilson of 
Stanford University.  He is an economist who advised the California Power 
Exchange and the California Independent System Operator on market design 
matters.  The paper compares the pros and cons of centralized versus 
decentralized pools, comparing the California market to many other power 
pools in the world.  While it is a bit academic (and California-centric), it 
is the best high-level characterization of pools that I have ever read.  
Forward to people as you see fit.