I'm interested in how the Dragonborn and Tieflings will be handled. I've always like the Tieflings in the Planescape setting - a race with a trace of fiendish ancestry. On the other hand, I didn't care as much for the 4e Tieflings. Maybe, it's because the Planescape Tieflings had varied appearance (reflecting their various fiendish ancestry) and came across as a little roguish, whereas I felt that the 4e Tieflings looked a little like they were trying too hard to be fiendish and bad@$$.
As for Dragonborn, I don't mind the concept, but I didn't like the 4e Dragonborn too much. That was mainly an artwork issue with me. (I know that it comes across as a little petty!) When I first saw the 4e Dragonborn concept artwork, I thought that it was artwork for lizardmen or Yuan-Ti. Where are they wings (even vestigial)? Where are the tails. Anyway, I thought that Monte Cook did a better job with the Dracha from Arcana Evolved. With different artwork and a better backstory, I can see the Dragonborn being a viable race for my campaign.
Just my 2cp