More than you think. Barnes and Noble could give away their Nooks and still make money from the content delivery side.
I think the media content is highly profitable 'today', but I think the content price is going to drop dramatically soon. I mean, with a paperback/hardcover you have printing costs, distribution, storage, shelf-space and damages. With ebooks there are a couple copies of a small file on a bunch of servers (for data security); and each copy is sent out 'x' times. No storage, no shipping, no printing, no shelf-space.
As Amazon, Apple, Google, Nook and others enter into this industry - prices are gonna drop and they can drop a LONG way.
And this doesn't count 'Overdrive' where you log in with your Library card - and can 'borrow' practially any book from a local library for 2 weeks at a time.