Thank you everyone, I'm not happy as it is still a bit "soft", but I think that is the lens.
Khol - the cropping is mostly the black border off to left and right, I don't think I took anything off the top and bottom edges, or if I did it was small.
800mm with the 40D is pretty much ideal (size-wise) for Moon (and Sun).
Bigger image here:
Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.