First, apologies for not getting back with my comments from the Astronomical Society sooner. To be perfectly honest, I completely forgot, but came across my printout of Steve's initial question while going through my file in preparation for this month's meeting.
I did read out the gist of what Steve asked, and received (ignoring the more flippant comments so typical of our members!) the following thoughts:
First, as already noted, the (present) universe is nowhere near old enough for any black dwarfs to have had time to form.
Second, "cinder" is probably a fairly accurate description, as the gravity would not really be high enough for the creation of diamonds - at least not at the surface. They may, however, have a massive (teracarat?) diamond at their core, but the surface gravity is of many orders of magnitude less than, say, a neutron star. Remember that the mass of these stars was only just enough to set the nuclear furnaces going, so not enough to create really mind-boggling (not to mention matter-boggling) gravititational effects. If you landed there, it is unlikely that you would be able to take off again, and you would probably lose a lot of height in the mean time, but the gravity is unlikely to be sufficient to spread you out into a monomolecular layer or to create a surface with a billiard-ball smoothness.
I stress that these are merely some of the opinions expressed by members of Cockermouth Astronomical Society and do not constitute an official statement by said society, nor are they backed by academic research into the subject.