I am not a fervent reader of XKCD but I do wind up on there quite a lot when their comics are linked from Digg or another site.  Anyway, I found this comic to be incredibly relevant to my own profession.  I bought the poster version of the comic and it is spectacular.

The poster has a lot of detail you just cannot see if the comic.  Everytime you look at the poster you see a new facet of the web of online communities you didn't see the first time.

I hope they make a sequel of this map next soon!  Maybe the landscape will change a bit...  if you know what I mean...