I am very glad the dragonborn are PHB-bound. I have been a big fan of the /idea/ of draconic PCs since Council of Wyrms in AD&D2 and thought their inclusion was one of D&D4's high points. I was fond of the playtest description of dragonborn -- that they hatch from specially prepared (or unprepared) dragon eggs and carry the traits of their dragon relatives -- and hope it sticks. I really hated that all the dragonborn in D&D3 were purple (as much as I love purple) and all the dragonborn in D&D4 were bronze (why bronze?!).
I'm hoping for a metallic and a chromatic subrace of dragonborn.
My first criterion for any RPG character species is that it be true-breeding and populous, which is why I'm not a big fan of half-orcs or half-elves. I have always felt like the former might as well be orcs and that you can get the same effect as the latter by playing a human raised by elves or an elf raised by humans.
That's not really my big complaint with tieflings, though, as D&D4 did (clumsily) rectify that discrepancy. I have the same issue with tieflings that a lot of you seem to share, which is that D&D4 tieflings just don't live up to the promise of the concept from Planescape.
I suppose that logic dictates that there be at least a devil-tiefling and a demon-tiefling -- perhaps the demon-tieflings could be the table-generated urchin-mutants of Planescape while the devil-tieflings remain the scions of Bael Turath, or what have you.
But tieflings also fail my 'Lynch Test,' which asks, "Would this species realistically not be lynched everywhere they went?" The tiefling works as a populous, true-breeding (more or less) species in Planescape, because part of their charm is that they are the /least weird thing/ about the setting. They are almost /expected/.
But on a prime material world -- particularly a prime material world in the grips of a "points of light" scenario -- they look an awful lot like an advanced possession victim. Keep in mind that the D&D world is /overflowing/ with dangerous humanoids that look substantially less blatantly evil than the tiefling. Why does the tiefling get special dispensation to walk the streets without harrassment?
"No, wait, I'm a tief-urk"
"Hello sir, I'd like to buy a week's worth of iron rat-urk"
"People of Geoff, I have slain the giant king, hey what are you doing with those-urk"