Somebody sneezed today and I wondered what my obligation to say "bless-you" was to them, considering the pysical distance and people between us. With that in mind, and in the spirit of the superb blog "Indexed" I came up with this:
I'm aware that there could be several more factors in this, but this is a good basis.

I generally avoid saying, "bless-you" at all times.
At every sneeze, I assume the sneezer has just blown snot all over their hand.
I prefer to provide them the privacy of disposing of that snot in any way they see fit, without my calling attention to their present situation by saying "bless-you."
salud... dinero... amor. What do we say on the 4th sneeze?