What's the most profitable price for an ebook?

That’s only true with a unique product or a noncompetitive market. Apple products? True. Commodities: False. Most products sold are priced by cost (material & labor) + competitive markup. In a real market, if you markup more than your competitors you lose business.

My guess is the $10 bubble is more a product of the fact there’s far more product offered at that point due to price fixing than there being a consumer driven reason for it. And a major reason for that pricing is still the publishers being afraid of fully committing to ebooks and cannibalizing the paper book market. It doesn’t take a marketing genius to figure their bottom line profits would be higher selling twice as many of a title for 60% of the former price.