Its changed over the years...
When I was between 0-8 I'd get one present the night before, my parents would rig it so it wasnt really a worth wild gift anyway, maybe just a pair of shorts, or an inexpensive toy.
from 9-18 it was nope, no way in hell are you opening anything till christmas.
Now, with a Family of my own I make the rules. We have 4 places to visit in 3 days, so my fiancee, our daughter and I do our own little christmas gift unwrap on Christmas eve because its just too difficult to pack everything up, unload it, unwrap it, load it up, go home and unload again...only the presents left from when Santa visits are taken Santa to our daughter to my grandmothers (or fathers depending on the year) and she opens presents from Santa, along with other gifts from my parents, grandparents and aunts and uncles, etc.