My DS has never opened his presents at the party, except for one time. His party has always been outside of the home so we always have taken them home and he has opened them there. At home I always take a note of who has given what gift and we then do up personal thank you notes, usually including a photo of the child who has given the gift at the party. When they are ripped open at the party, you can not remember who they are from and I like to thank them and actually mention the gift given.
I don't think it is rude not to open the gifts at the party, my DS has not been to many parties where the gifts are opened at the actual party, unless the party is held at home. But when the party is held at a theme park, play centre of venue of some description it is hard, things can get lost and the parties are usually organised and timed and there isn't usually present opening time scheduled at the parties. I am not offended if the presents are not opened when my DS goes to a party and my DS doesn't care either, they are so used to not opening, you see the kids look for the present table when they arrive at the table, they just want to run off to play

Plus if there are only just a few kids at the party its ok but if there are a lot of children, 12 to 30+ then often the guests don't want to sit around for that long watching someone else get the presents, they want to play

(and get their own take home favors

).
Anyway, it does not bother us what people do when we go to parties, I think it just depends on the person and the location of the party, there is nothing wrong with opening them at the party and there is nothing wrong with taking them home or opening them later.
