I learnt on hard (6000ft) runways but now fly out of Netherthorpe with the shortest (licenced) grass runways in the UK.
Apart from being bumpy, the main difference I find is the actual take off. On a hard runway you make a (gentle but positive) rotation by pulling back on the yoke at the appropriate speed (say 55kts in a C150 without flap).
On a grass strip, common practice is to use the soft field technique, i.e. pull back slightly on the yoke to lift the nosewheel clear of the grass to reduce drag. This tends to result in the aircraft flying itself off the runway, and so care is needed to level off when clear of the grass to allow the airspeed to increase - otherwise a significant risk of stalling may occur if it is gusty.
Combine this with the bumps, and it seems as though you actually do about 10 take-offs and 9 landings in every take-off run....
