I think to blow ones nose into your napkin is very poor manners. I agree that sometimes a sneeze or something may cause you to have to cover yourself with the napkin quickly but that's the exception rather than the rule. Blowing your nose into you napkin leaves a host of germs, the waitstaff handles it, then maybe after they've handled your snotty napkin, they handle someone else's dessert, etc.
Who wants to sit and try to eat while someone is blowing and gurgling into a napkin or handkerchief--what irks me is those that blow, look at it, fold it, blow again, look again, then wipe their nose and then stick it back in their pocket or lay the napkin on the table.
If I have that much of a problem I'll stay out of the dining room to begin with.
At Cracker Barrel once we were having breakfast and this older couple were seated next to us basically within arms reach. Being from a rural area we grew up eating lots of mom's biscuits and gravy, which I still love today and was part of my breakfast that morning. This one older fellow would take out his handkerchief every couple of minutes and honk and blow, look at it and refold, do it again, etc. it seemed every time I started to take a big bite of biscuits and gravy is when he would have to blow and gurgle into his hankee. Finally I told him that if he didn't stop blowing and gurgling while I was trying to eat that every time he blew his nose I was going to loudly pass gas and point at him !!
He got pretty upset but didn't say anything and kept his hankee in his pocket for the duration, so apparently it wasn't needed as badly as he thought it was. There's a time and place for everything and snorting, blowing and gurgling mucus at the table isn't one of them.
Just my humble opinion--I said it--I read it and I approved it !!