My missus has a real issue with this and throws away a fair few future family heirlooms due to this, citing hygiene as the main concern.
Personally, it doesn't bother me at all.
I only say this because all the cups at work are fucked if you're not in by 7am.
Where do you stand? Do you care?
I think I need meths to be involved in this thread for it to be successful...