Like OP, I never saw my parents open gifts until as a child I was old enough to either make them something or as I got older buy them something. Don't get me wrong, they bought each other stuff, they just did not wrap it & put it under the tree, they played with it or used it pretty much immediately. DH said his parents have always done it that way also.
DH &I get each other stuff, but we don't wrap it and put it under the tree. a year or so ago, DH & I took the boys out w/o the other "parent" and helped them buy "dad" something (he did the same) and then I helped the boys wrap dad's present and he did the same, but thats the only presents for us under the tree... now, we exchange gifts w/ other family members and the kids see us unwrap those presents, but once we had kids, we rarely wrap anything for each other and put under the tree... we just get it and
start playing with it immediately.

I already have my Christmas Present for this year... DH & I got each other (and the boys) a family trip to WDW 12/27-1/2 w/ dining plan (paid cash in full back in Oct).. we have a gift card to cover the cost of increasing our tickets from 6 day plain tickets to annual passes for the 4 of us and a gift card for any extra expenses including souvineers, and I got a new Canon Digital SLR camera (the T2i) w/ various Lens', and DH got allof the above (except the camera) and an invicta watch he's been wanting... (yikes, this year, we were a lot more extravagant with ourselves then we normally are!) none of this will be wrapped and under the tree, but the boys are well aware that it's mommy & daddy's presents to each other.
I took DS's out and we got for Dad from them Seasons 1-4 of Burn Notice on Black Friday for like $5.00 each and then we got him the camera and remotes etc to make his PS3 that new motion technology (thats sort of a gift for the boys also, but oh well) DH took them out yesterday and I know they came back with some stuff for me, but I won't know what it is until Christmas morning. then DH & I together will take each son out and help him buy his brother a gift that will be wrapped and under the tree. that gives our kids one on one time with both parents which is rare! our boys also do all our family shopping with us.. we try and emphaize the shopping and gifting for others much more than something for ourselves.
DH & I were actually talking about this last night! we always felt sort of silly before we had kids wrapping things & putting them under the tree, and most times, it did not make it to christmas morning! .. he'd say something about needing or wanting something that I already had for him and wrapped under the tree and I would be like here, open this.. no sense waiting, and he was always the same way... It works for us but we also recoginize that other familes do it otherways that that works for them.