I love to block out movement and logic in the game engine before adding complex graphics. It's so quick and gratifying. Once you've got everything working how you want on a cube/dummy though, how do you replace it with your final character / mesh? Easy! Just copy the logic bricks over by:
1. Selecting every object you want to copy the logic **TO**.
2. Select the object you want to copy the logic **FROM**.
3. Ctrl+C brings up the copy menu and just select "Logic Bricks" (you can also copy all kinds of other attributes here).
Why the weird order of selecting the "paste" object before the "copy object"? Because this way you can select a bunch of objects to paste to first and copy logic from one object to a whole bunch of others in one go... Sweet!