I know this is coming a bit late and I know this is a bit off topic, but I had this question specifically concerning citing Kindle or iPad ebooks in MLA format.  I have students using their Kindles and iPads and this question has come up quite often.  I asked a professor about how to cite those editions in MLA and more specifically about the reference locations.  He was unsure about the reference locations (and said he would check on it), but this was the response I was given by Dr. Jim Harner about citing them in MLA and I thought I would share it:

Several people have asked me about citing a Kindle a la MLA. I contacted David Nicholls at MLA: he reported that MLA is working on a form that resembles he citation of a non-periodical CD-ROM:
Author. Title. Publication information. Kindle.
Until that form is finalized, he said MLA is recommending using the form for citing a digital file (6.8.18 in the MLA Style Manual; 5.7.18 in the Handbook).
Jim


Best,

Shawn W. Moore
Ph.D. Student
Department of English
Texas A&M University