1. The price.
The books need to be a lot cheaper digitally, and they don’t seem to be at the moment.
Also, £200+ for a device to read a book seems a little expensive, especially considering that..

2. It’s only mono. I don’t mind reading the news or fiction in black text, but a magazine without any pictures would be unusual.
It’ll be a lot more interesting when they start using colour eInk.

3. Sony/Kindle, and others are currently all supporting different formats. Amazon isn’t the only place to buy books, which is good considering the format they use isn’t readable on the Sony Reader (for example).
They need to agree a format first.

Then I’d be very very interested.