Only useful if you connect it in a way that makes it replicate.

WiFi Mesh networks are what you're thinking of here, and I've been thinking a LOT about this watching what happened in Egypt with the internet kill switch and reading in the news that the current majority party in the house is introducing a bill to try to get the same kill switch setup here in the USofA.

An ad-hoc wireless network running on cheap/older hardware, with "store and forward" routing sounds a lot like the old BBS platforms I used to frequent, in particular Fidonet is very close to this idea.

The main thing is Replication - like lotus notes used to do. That way you can get data, and replicate it in case your own connectivity is limited or cut off.

Bittorrent is also a very, very nice protocol for replication of data sets.