Yes, the API is limited... Writing to SD is not allowed. But from what I have read, reading is permitted (I've not tried it myself). SD support would be a good addition for a future update, though. I can see where it would be nice to use a PC to put a book on the card, then read from the app.
I just bought the app, sight unseen. I like to support devs who post here, and a buck isn't much to pay. I'm about to go to bed, though, so I'll try to remember to load up a book in it tomorrow. I've got several ePubs in my SkyDrive, that currently I use Freda to read.
To those who want the SD support, yes, this is a good idea. But something to keep in mind is that for any app, the most important feature is that it ships. If a developer keeps working on an app without shipping it, adding every feature that people might want, the app will never ship, and you'll never get to see it. It's better for a developer to ship something basic, then take feedback, and implement the feedback that is most desired. :wink: