D.P.
My son is 8, he's attended about a zillion parties in his life, but I've only seen kids "play" with the gifts at maybe 2. Usually, they are opened, oooooh'd and aaaaah'd over then they are packed into a car.
And I'm all for opening the gifts at parties--the kids LOVE to see their friend's reaction to the gift they picked out especially for him/her!