iBooks Author: Publishing and distribution FAQ
http://support.apple.com/kb/HT5071

Can I distribute works created with iBooks Author as part of a product or service that charges a subscription-based fee?

Books created with iBooks Author may not be sold as part of a subscription-based product or service. iBooks Author books must be distributed free of charge or made available for sale via the iBookstore.

(via Instapaper)

Sent from my iPad