I don't have it, but a member of my yahoo stroller group says it is great on grass, sand, etc. The only thing that prevents me from buying it is the fact that the front wheel does not turn, so you need to lift the front of the stroller to turn. My kids wouldn't appreciate sliding back-wards as I lift.
Have you considered the Pet Gear AT3? It has the larger wheels, and the front wheel turns, and has a lock, if you want to go over rough terrain.
Sheila