I'd say it's closer to 1:1 or 2:1 considering what Iv'e seen in the wild. Other systems can advertise books right in iTunes like a single app. Kindle has to be discovered via Amazon's site so it really only appeals to existing customers. Apple has way more brand recognition.

Really? They both play this kind of stuff close to the chest. As far as I know Amazon has never released sales numbers for the Kindles, at least Apple tells us that.

Anecdotally I use Kindle ecosystem, as do some of my friends and family. I don't know anyone who uses iBooks, so that's probably skewing my viewpoint.

I guess they did at least make a name for themselves with textbooks, at a minimum.

EDIT: According to All Things Digital, during the trial one of Apple's people estimated their market share at 20% [1]. That's way higher than I would have guessed.

[1] - http://allthingsd.com/20130613/apples-e-book-market-share-is...

This just goes to show you the power Apple has over the market with their platform. They enter a new market and now they own 20% of it and are signing price fixing deals with every publisher a year later.