I find, for myself, it is quite easy to tell which way up a micro USB connecter is, even in the dark. The bottom sharp corners to me feel much sharper when pressed with a finger than the upper rounded corners do.
It even works with the very few connectors I have come across that have the USB logo on the bottom
instead of on the top
.
Has never failed to work for me, but I am sure there are some around who will find otherwise (or who cannot remember their up from down).