A new image of the new creature - commonly referred to as "Endermen" - was released recently (enhanced here, for light levels). This image is much more up-close-and-personal than the first, giving us a good look at the new creatures. It would seem that wearing a pumpkin prevents the new mob from seeing you, although this is unconfirmed at present.
Additionally, Notch mentioned a possible name-change for the newly minted mob, "Farlander" being suggested and, apparently, already in heavy use.
We have a poll for the creature's name, check it out! Response to the poll was so overwhelming that it actually overflowed what the poll was capable of storing! We have fixed the poll - however, any previous votes will have to be re-cast. We apologize for the inconvenience!