"If it wasn't for those damned laws of physics always screwing up my plans..." basically. Mesh networks have a pretty hard constraint of k/n^2 bandwidth total where k is an average node's bandwidth and n is the number of nodes. You quickly get down into the 'bytes per second' range.
Summary: Throughput of a mesh asymptotically approaches 1/7th of the non-mesh link rate. This is using the 802.11 MAC, but recent softMAC chipsets could be run in a more mesh-optimized psuedo-802.11 protocol (that has not been invented yet AFIAK), so you might get performance as good as 1/4th.
