I liked BlackBerry10 picture passwords [0][1]. Unlocking was a bit slower than drawing few lines but good enough to unlock device fast - I'd say even if you were weakened by some disease/illness/exhausting workout moving slowly a number to target is easier than drawing few crossed lines.
I once got a friend's iPhone passcode correct first try by looking at finger smudges. If you're entering a passcode frequently it's definitely a risk to be aware of.
Yep, pretty easy to do - especially if your pattern is recognizable or doesn't cross over itself.