When it comes to the look of Tieflings, I am going to have the characters decide what to look like since I am not basing my Tiefling history off the core-books.
However, for the tails/horns comments, I think if I ever go that way I am going to do it like this: When they are young their horns and tails are underdeveloped and very small and weak as they grow they develop as the Tiefling develops who he/she is... So a sneaky, roguish Tiefling: small horns swept back behind the ears and a agile prehensile tail. A blunt, fighter Tiefling: larger ram style horns and tail strong enough to whip at enemies.
As for the history, it is a pretty common archetype, really what it comes down to is a much larger scale version of "the sins of the father passes down to the son." It is something that has been around FOREVER, and is just equally common to have those characters either rebel against and meld with that past.
As for Vampire, I would say outside of D&D, Vampire and World of Darkness in general is the most popular PnP. You can tell that it does have a fairly large popularity by the fact that White Wolf has actually been doing better since they nuked their last World of Darkness and started the New World of Darkness.
Which in someways is what WoTC I imagine is slightly trying to do with 4e. Taking all the old-races, etc. that we love and giving them a fresh light. Like White Wolf did with Vampire, Werewolf, Mage, and Changeling. While the new setting each-year, is reminiscent of White Wolfs, new game each year, with the first being Promethean, then Changeling and next being Hunters.