Yeah... while it's interesting in a theoretical sense, I don't think HDs, at least not using current technology, will ever get anywhere near that kind of theoretical speed.
And although it's generally true that once one line of technology tops out, it's replaced by another, there are physical limits that those pesky natural laws impose (such as this speed limit). Although you could, in some cases, push them a bit, it's usually not worth the vast expense to do so.
Hence passenger planes haven't gotten significantly faster in three decades and the only one that was is now mothballed. Cars can go a bit faster, but a high-end racecar of 40 years ago isn't that much slower than one now. We're still in the infancy of computer tech, but it's much more mature now than it was in the past.
Note, for example, that the rate at which the density and speed of ATA hard drives increases has fallen off considerablly in the past couple of years, and SCSI has been relatively stable in terms of density and speed for going on two years now, with no technologies anywhere near the point at which they might take the place of current platter-based rotating magnetic storage. Even Hitachi's 400GB monster just uses 5 platters with the same tech as the 83GB/platter 250GB drives.
Not to say that advances aren't being made, but Moore's law and its kin aren't some set-in-stone law of nature, it was just a worthwhile observation about the advances in an industry in its infancy that held true for a while. Every tech advances rapidly in its infancy, after all.
