Wow! Fantastic Contraption has grown up :)
I think I speak for most people when I say. Please don't publish untested levels, and if you must, add 'untested' in the description. I don't mind spending a long time finding a solution if I know one exists. But when you waste hours believing there is a solution, and it's impossible, I get pi$$ed!
I vote for a tested only section where levels that have at least one solution can reside.