Not to belittle the great achievement made yesterday, but are the SS1 concept
and materials usable for real space flight ? Or is this a design that is
really limited to the Xprize mission ?

From what I heard, it only reached top speed of about Mach 3. Is that correct
? So from a re-entry perspective it is quite far from orbital re-entry. Does
anyone know if the structures/materials would potentially be usable for much
faster re-entries after a real orbit ?

Did the flight just go vertical, and when it ran out of fuel, just had gravity
decelerate it and it then began a vertical free fall back to earth ? Could
such a trajectory really be considered sub-orbital ? (seems like just shooting
a bullet in the air and letting it fall back).

I was under the impression that sub-orbital meant that the speed would be
mostly horizontal with just enough vertical thrust to maintain altitude since
the vehicle woudln't be going fast enough to be in "orbit".

If I remember correctly, during re-entry, the shuttle gets to "re-entry
interface" at 400k feet, which would be 123km altitude. So, at 100km
altitude, would SS1 have been totally under RCS control, or would its
aerodynamic surfaces still have had some effect ?

(Again, I don't wish to belittle this achievement; the nitrous oxide rocket
(laughing gas) seems like a big advance in rocket engine safety, and the
ability to generate a mach 3 vehicle at such low cost is also a great achievement).