when people upload to Debian with an @ubuntu.com email address
even better, if they do that when they are DDs (so with a @debian.org address)
Yeah! Actually, doing so shows several things: That the collaboration between Debian and Ubuntu actually works out. That people that feel more attached to Ubuntu also do care for Debian. And that those people started to realize that contributing things back to Debian actually does reduce their own workload with respect to not having to maintain seperate patches, with the benefit of all involved parties.
So big kudos to you people being able to look over the corner of your little universe and see the bigger picture for the benefit of all!