You know those ads are so obtrusive that when HarryT said there was an ad at the bottom of the library page I had to go look as I didn't recall ever seeing it.
Obtrusive means almost invisible right?
As to can only put Amazon books on a Kindle, hmmm. I have put books from PG, Smashwords and various authors on my Kindle.
That is on a special offers, not jailbroke, or modified in any way Kindle.