JohnK, I'm probably a week late here but I've put in probably 50 or more grain bin floors. If it is plank style, I bet it would make a nice dock. The newer style bin floors are designed to make a smooth surface for easy sweeping. They are perforated to let air flow through or in the case of a dock, water to drain through. They are galvanized and snap together. You wouldn't want to cut many with tin snips, a partner saw would be ideal. The only problem I see with used flooring is that it may be bent up from disassembly and not fit back together well. The snap together very tightly with interlocking Js. Another problem is that if it came from a round bin, there won't be very many long ones and if laid end to end usually leaves a very sharp edge that has to be covered.
I think it's a great idea and will seriously consider it for the floating dock I am contemplating.
Here's a link for the type I used to install
http://www.brockmfg.com/uploads/pdf/BR_2051_0308GrainBinFloorsEM.pdf
