Also this, if you've flown a retract or been with someone that does, is where the philosophy for not touching anything until off of the runway and coming to a full stop comes from. As long as that microswitch is functional, the gear shouldn't retract if you put the handle in the up position when at a full stop. Those microswitches do gum up at times with dirt and other crud, but they seem to keep going mostly.
Early Beech aircraft, specifically the Bonanzas, put the gear and flap handles, right and left, respectively, opposite to other manufacturers. The handles are dissimilar, but not so much that you might grab the wrong one. Newer planes attempt to stop this with differing methods. The PC12, for example, had a huge wheel-shaped gear handle and a smaller flap-shaped handle down on the pedestal.
It is accidents like this, along with aerodynamic improvements and COST, that encourage the manufacturers to shy away from retracts.
