Recently, WotC moved their 4E Character Builder online which means they have access to all the characters people make and play, thus they can analyse what is being played the most, which options are popular and which aren't. Over at D&D Experience they let slip a bit of this info. Quite unsurprisingly, the most popular races are:
Human, Dwarf, Elf and Eladrin
(for 4E newbs, the Elf is your old Wood elf variety and Eladrin are High elves)
It would be interesting to see what the fifth most popular race is, but whichever way you turn it, it's clear that the classic old triad of Human-Elf-Dwarf is and remains the most popular by far.
The most popular class is...*drumroll*...Fighter. No matter how many cool new options and classes, divine, arcane, shadow, psionic or whatever heroes they offered, the Human Fighter remains on top. Pretty interesting.
The least popular class is the Runepriest. I even forgot that existed. I don't even know what it is. I guess it's just not appealing.
It would be nice to see WotC release more of this info.