The keys are hard plastic with a rubber conductive membrane, pretty much like the primary action buttons. Last we heard the membranes weren't ready yet, so nobody knows exactly how the keys feel. You can see the keys themselves still in the molding frame on Craig's desk on the openpandora.org blog.
I asked before about tactile feedback on the keys, if I remember, they said they would be quite touchy-feely
EDIT: Alright, found my thread
craig said:
This is something which is being worked on right now, most likely they will be similar to the keys on a P300 samsung phone, a membrane coated in a plastic where the keys are, something like 1mm max movement but with feedback when you press them.
They have to be very thin and this seems the best way of doing it, of course this could change later in the month, if anyone has suggestions based on maybe work they have done on such devices we would like to hear from you
The easiest way to describe it is as "squishy" as opposed to "clicky". If you've ever played a 360, go push any of the face buttons, then hit one of the bumpers. The face buttons use the thin plastic membrane to complete the circuit, whereas the bumpers use tactile switches, which produce a mechanical and clicking feel/sound.