Can someone explain to me how p2pool works?  How is it different than a regular pool, and what are the pros/cons?

Thanks in advance!

edit-- nvm, did a quick google search. -.-

Well, can someone explain to me how to go about picking the best p2pool?  I don't really understand how to go about choosing one (or are they all the same?).  What should I be looking for?  My hash is about 2.2 Mh/s