We don't really have a rule. The xmas before DS was born, we got a joint gift - a digital camera. Come to think of it, I think I paid for that!!!

Our DS' first Christmas we went back home to CA - so I think that was what we called Christmas.
Last year I got him new speakers for his car (pretty cheap as I had a friend order them and he put them in for free.) I think I got him some socks and undies. I'm sure I got him a few other things but I really don't remember. I put a few things in his stocking, no big deal. I did really want to get a camcorder as a joint gift again. That didn't happen. Quite honestly, I don't remember what he got me besides the socks I asked for...

This year, I said we should buy each other gifts in January after I find out if I still have a job. I work for one of the big 3 and we are downsizing. I am the primary bread winner, so its going to rock our world if I don't have a job. If I survive, we are again talking camcorder (ok, I am) he wants a home theater system and I'm talking maybe a Bose docking station for my iPod that I just got for FREE!
Next year (again, if we are able to keep our jobs) we will be going to CA as our DS has only seen some relatives (aunts, cousins, grandparents, etc.)once so far. Its a very costly trip purchasing 3 tickets and renting a car for a week. We will *have* to take our DS to some of the local attractions (I'm sure Disney will be in order) but I'm hoping we can get grandparents to pay for that.
