Just for grins, I just plugged a 8GB SDHC card in my Cybook.
Didn't work, of course. But the funny thing was that it didn't simply ignore it, like I expected it to. Instead, it hung at the bootup screen, as if it tried to make sense of it and failed.
Might the fact that the SDHC card was at least in some way visible to the Cybook mean that the SD controller is indeed SDHC capable, and the software is just not yet able to drive it as such, much like he Nokia N800?
Probably too much to hope for