Congratulations! Our daughter is just over six months old and our three year old boxer Leroy has been fantastic company for me - it's nice to have a friendly soul around the house when things get a little crazy! We did all the blanket/nappy smelling etc but Leroy didn't seem that interested - he was more excited to see me home after three days. He has got very protective of the house (and us in it) but it has taken a while for him to work out that the baby isn't a tiny adult (eg won't play when he drops his toys on her head).
My biggest worry was that he would be all over the place when we walked with the push-chair (you know what boxers are like - they'll trip you up just to get to a bit of paper on the other side of the footpath...) but he walks perfectly alongside and rarely stops to sniff the flowers like he used to.
In reality though, Leroy has had a LOT of adjusting to do in terms of not being #1 baby anymore, and of my time being taken up with a squirmy crying thing who has ten times better toys than he does (and gets fed a lot more frequently). On the upside, he has me home all the time, we go for a walk at least twice a day and heaven really is being under the high chair when food gets dropped over the edge...
Good luck with your baby!