[TechniSol]

I'd add that most smaller cards (4gb) are engineered to move smaller blocks of data around, and those faster class rated large cards are not nearly as efficient at moving smaller blocks around as they are engineered to address larger blocks of data. Rather than a class 10 rated larger card you may be better off with a class four rated card, it certainly makes reading a few threads addressing this issue worthwhile before buying a card to see with which ones others may have found success.

PS The real solution is for Kobo to fix their approach to scanning the external SDHC/maintaining the database on the device. I sometimes wonder that they've taken the approach they have because some marketing tool built a survey designed to show that most people only changed a few books at a time and wouldn't really use the extra storage anyhow...