Several months ago, out of curiosity I loaded a few manga pages pages on my K2. You can see the images in my test album
here.
One of the issues was the all the white space around the margins made the pictures too small and type too hard to read. The Kindle has been upgraded a few times since then and now with PDF support maybe a properly cropped version would look much better.
I'm sure some who has real experience with manga on the Kindle will pop in. While waiting, if you have something you want me to test for you, I'd be happy to try.