It's been a long process but were finally in the implementation stages of our Outdoor wireless mesh. We've designed the system using Cisco Aironet 1500 Series AP's and the Cisco Wireless Control System (WCS). Our first phase will include (7) Access Points mounted on 15' poles and (2) of the WCS base units. There will be a back-haul on both sides of the mesh and all AP's are within (1) hop of a back-haul. They say you can put the access points up to 600' apart but we decided with all the tree's on campus to put them 300' - 400' apart to be on the safe side.
With the Cisco 1500's the AP's talk over 802.11 A and the clients can connect over 802.11 b/g
From the picture below you can see a basic layout of the mesh (I threw it together in Visio using the sprinkler heads for access points so I could visualize the bubble). Backhaul locations are in both corners top right and bottom left.