Communities

Hi, I'm looking for information about the way networks use communities in BGP. It seems that many of the larger networks only use communities to supply their customers with a mechanism to adjust the local preference to indicate which connection is preferred when a customer connects over more than one link (something that can also be done with the MED). How many networks are there that use communities to indicate where (which interconnect point) a route was learned? And how many networks use this information if their upstream provides it? And how about things like congestion? Is there any need for more "well known" communities? TIA, Iljitsch van Beijnum