[ProDigit]

Just to mention:
There have been 2GB SDHC cards manufactured, one needs to read what the card says (SD, SDHC, or XD)!

Another thing:
Most micro SD cards of under 2GB are way cheaper, even with an adapter.
One can easily use a 1 or 2 GB microSD card (non SDHC), and plug it in a micro SD to SD card adapter.
Many websites throw microSD cards in your face (with adapters), because they hold very little value for a customer nowadays (people want 4,8 and 16GB cards for multimedia)!

It could save some money buying them instead, especially for someone in the future trying to do something similar than this, and even a 512MB microSD card is large enough to do a firmware upgrade, and store quite a large library of books on!

Also microSD cards generally consume less power than regular SD cards,they are a bit slower in writes though, but it should save you 'some' power when reading books from them.
Then again, if you want to save most power for your reading device (maximize battery life) there may be devices out there, where it might be better to store the books ON the device, instead of on an external card.