Not directed at anyone in particular but I sometimes notice at friends or family's houses that the sponge is usually kept at the bottom of the sink or floating in a bowl of cold, greasy washing up water.
My thinking is that, logically, anything that scrubs your plates/glasses/cutlery should also be clean enough to put in your mouth. All I see with the floaty or sink-bottom-dreg-filled sponge is a bacteria factory (especially if it's a meat eating household) but it is so common, I wonder if I'm the odd one here?
Disclaimer - My sponge-in-sink aversion doesn't affect what I think of the person (or stop me eating there etc). In fact, I think most of my favourite people keep minging sponges. I am also no clean freak and know that there are loads of things in my house that other people probably find disgusting (actually there are quite a few filthy oven, frequent horrendous slimy leftovers in fridge that I find disgusting myself but not enough to bother doing anything about on a regular basis
). I am, however, scrupulous with rinsing, drying and replacing my sparkling sponge.