I feel I MUST vote for the leaves since the timer leads to a slightly annoying trend I face often at work. PLEASE, If the microwave is used by other people besides yourself, CLEAR THE TIMER. Seriously, it is a single button push before you turn and walk away. Have some courtesy, don't make the next person need to clear your settings before they can use it.
Again, I know it is not much and I probably should not be making a fuss over it but please, clear your left over time. Side note, Some people also tend to use a microwave clock as a time keeper, so leftover cooking time prevents that as well.
Thank you for listening to me rant, I know this may not be the right place for this so a preemptive sorry.