That horseshoe must be so far up that you can see the imprint in his forehead.

putting metal spikes under the floats might help

I worked as an engineer for a company called Ontario Central Airways which moved from Reddit and Kenora to Gimli Man. All our float planes were landed on the grass in the fall and after winter maintenance taken off from a dolly in spring. Cessna 185's and smaller were pulled down the runway with a jeep, larger planes with enough power and rudder took off on their own power. The noise of the exhaust of a 185 along with the prop on top of the metal roof of the jeep was something to hear. Superior Airways in Thunder Bay used a dolly that was pushed from behind and some fool stood in a 45 gallon barrel with a Skidoo helmet on and held the tail of the aircraft to keep it straight. I've uploaded a few pictures in the albums section.

saw a guy do it once in his 185... and like was said earlier... the grass had to be wet. (it had rained all day prior to his take off, and he used a whole lot of turf)

He seemed to have good directional control... but I'm guessing he just got lucky.

I've landed and taken off numerous times on frozen lakes. A good thing to keep in mind is that there is absolutely no shock absorption, so you need to do it gingerly and make sure that there are no deformities on the ice. Trying to rotate is a bad idea, let the airplane fly itself off as slow as possible and it goes ok - directional control is not an issue provided you are into wind and there would be no reason to be out of wind. Obviously it is hard on the floats in general, not something to get in the habit of doing. I have tried to launch off a grass infield with a stoneboat with the grass wetted to save dollying to the nearest lake. No go, the boat would not budge an inch. I have seen pics (actually one of their calenders) of Wardair from Juneau with their fleet -3, -2 and 185 parked together on the Juneau icefield on floats. That was pretty crazy stuff and a pretty needless risk imho.