There is still the fat-finger problem, which the users’ finger occlude a target they are about to touch and it causes inaccuracy/error, exists on Kindle Fire. In addition to this article, I would like to say that touchable area mappings on Kindle Fire and iPhones/iPads are slightly different: actually iPhone’s touch area mapped almost 5-6 mm lower than a graphical object, while Amazon Kindle mapped a bit more above than that. (See Holtz and Baudisch, 2009 to understand the reason behind this offset)
Since iPhone/iPad/iPod touch interaction is de-facto standard in mobile touch device world, such a deviation could cause user confusion and unnatural feelings.
Amazon Kindle Fire came to multi-touch device market much later than Apple. Amazon could have taken advantage of newcomer’s flexibility by putting much ambitious design in their design, but what they brought is quite conservative design, which, in fact, is much less cooler than their competitor’s device in my perspective.
Source: Jacob Nielsen’s Alert Box