There is no meaningful Kindle infrastructure to talk about if you own only one device. In my case, I had Kindle on an iPod, iPad for iOS. One session for my Android Phone. Two incarnations for my Desktop PC and Notebook and finally I have the Kindle 3G, Touch and Fire.
I have culled most of them. Now I am living with one Android, two Kindles, and the Desktop PC and Notebook. Mostly I am using the Kindle Touch, Fire and Desktop PC.
When plugged to Amazon's ecosystem, they work very well. It is quite a different experience when I try to use non DRM mobi books. Previously I could copy the books and their annotation files across my devices except the iOS easily. It is much more troublesome now. Kindle Touch has its own peculiar file system. I can no longer interchange its annotation files with the Desktop and Fire.
Kindle Fire is odd too. It would not accept annotation files from the Desktop unless I create the file with the Fire first and copy it over to the Desktop. Afterward the annotation file can freely be copied to each other!
It is such a hassle.
Furthermore the user interface of the Kindle 3, Touch and Fire are dissimilar enough that you have to learn and remember the differences. Sometimes I confuse them. I have given away the Kindle 3 and so I need to tangle with only two Kindle devices.
I tried to send my mobi files to the MYK space on Amazon, but it fails to synchronize the annotation file. This option is dead.
Amazon needs to come up with many software updates to improve and put every platform and device on the same page. It is here that Apple regularly beats the competition hands down. I get the impression that Amazon was behind the curve and desperately trying to catch up with Nook and the iPad in the eBook domain. It is their superior ecosystem that tilt the marketing mix in their favor. It had bought Amazon enough time.
Looking ahead, I think we will be spoilt for choices. A sizable consumer base would be willing to trade away the features rich iPad for a much lower price point with limited and focused functionality. I am happy with the affordable Kindle Fire that allows me to read books and use the internet browser. I am not going to pony up the extra for the iPad.