I think it's so important for the pet issue to be brought up when first dating. And many other issues, too. What's the point of "falling in love" with someone, if you're going to spend your life battling about the things that really mean something to you?
DH and I both grew up with dogs, and loved having them in our lives.
But we're also relatively practical people (in some ways), and after having our cat and all the issues she caused, we know very well that having a dog is too expensive for us right now. And we would have to choose the breed carefully, because there are some dogs I'm allergic to and others I'm not. I refuse to drug myself - I spent my teen years drugged out of my skull for allergies and I won't do it again - and there are no guarantees I wouldn't be allergic to a carefully chosen dog...we just need to wait to make sure we can truly afford the dog AND to keep me healthy at the same time.
DS really wants a dog, now that he got over the trauma he experienced when visiting my dad and his 2 big, untrained, messed up, goldens...he saw one of them "biting" me. She was actually mouthing my arm, not biting (though I wasn't moving, so it didn't become a bite), but DS was only 3 and was standing inside watching through the window...it really messed him up about dogs for awhile.
Anyway, we've let him know that we won't get a dog for awhile...our condo won't allow dogs of the size DH and I would like (malamute, GS (though I actually am not a fan of that breed, DH grew up with one), standard poodle) and we'd really have to change our brains to adore a small enough breed...DS also knows about the allergy problem.
And just the other day he said that he would have to make SURE that person he marries is not allergic to dogs, so that they could have dogs.

Ya gotta have those important talks, BEFORE you "fall in love"!