I've a K4, and have just offered improvement suggestions through the Kindle help contact on the Amazon WS - the newest will concern the Keyboard which is mistakenly setup in alpha order, starting in the small letters where it should be starting in Capitals and the old familiar typewriter keyboard style.
The others I kept a copy of, which I offer here for the perusal of those who may be interested:
The K4 (and all other Kindles no doubt) need software improvement for which I have FIVE suggestions to greatly increase functionality:
1) When searching, the ability to search within the books as a group is nice, but I'm usually looking for a book title, which the software does not do - please provide the latter option as well.
2) when backing up a page within a list of titles I'm always returned to the top of the previous page - this is inconvenient - it should be returning to the same line I was on before I advanced to the next page.
3) As a personal preference some readers might like to be able to keep their open page visible while checking a list or searching notes or the like - the ability to split the page in half and do both might be greatly appreciated.
4) Making Collections and adding books to them is needlessly awkward in several ways - the right way to go about this is to have this function within the menu, usable from any line of a book list as well as within the book itself. This should provide an ancillary menu showing up to a possble limit of 20 collections (in 2 columns) with check boxes so that one may merely check or uncheck any existing collections desired, the last entry being NEW collection which one would type in the name in when finishing one's entry. Currently I find myself going through the list of books over and over, uncertain whether a particular book is already in the collection I'm trying to work with or in any at all!
5) I would also like to be able to add additonal screensaver pages - is there, or will there be in the future, the ability to add additional screensaver pages - for example a favorite photo or bookcover.