These 4-6 MB books that I got are books with embedded fonts and some promotional pics. These are very wellmade books from a
german publishing house.
Personally I agree with ProDigit, I prefer small and simple books at my Kindle. But on the other hand: Large files can be fun, too.. I have no seize restrictions on my SONY, since I can put a Micro SD card into it. And some books look really cool.
This is not really a problem of the file seize. This is a problem of Amazon that won't allow us to put a Four Dollar Micro SD card into our Kindle. Which is quite weird..