This is all very interesting and would be very fun.  HOWEVER, check your 
Service Agreement or Terms of Use from your ISP.  I doubt that almost 
everyone on this list would be in violation of your sevice agreement if you 
started sharing your connections.

In fact, my service agreement stipulates that I can connect only one computer 
to the DSL and that the computer must be a Mac or a PC running Windows 95 or 
newer.  I am in violation by running Linux!

Now, if some neighbors wanted to create a "LAN" between their homes but not 
actually share their internet connection(s), that would be OK.  But that 
takes some of the "shine" off the idea in the first place.

I guess all that I am saying is that you need to know the risk you are taking 
if your service does not allow sharing your connection with others.

Alan