I was raised with the idea that discreet dabs at the table are acceptable -- spicy foods do cause one's eyes or nose to water a bit -- but real nose-blowing, like other grooming activities, needs to be done in private.

As noted in the other entry, in my family we make an exception for colds/allergies during at-home dinners. If you're blowing your nose every minute, excusing yourself from the table to do so is impractical. It's a little gross, but part of being family means putting up with a little grossness. (I cannot wait for my youngest to be out of diapers!)