I tend not to like the included faces in the kindle device. The serifs are knobby and blunt and although that helps with clarity on low resolution devices, they are highly novel and conspicuous to my eyes. I find myself constantly critiquing the kerning and the letters C, c, a, and y bug the hell out of me.
Still, I prefer it to many of the typeface choices made in print, especially some of those chosen by indie publishers.
I'm pretty conservative in my personal preference for reading type, Caslon and some iterations of Garamond are as near to perfection as you can get when it comes to body serif faces, but obviously the relatively low resolution of current e-readers render these types horribly unless you read at 18 pt.