I have often checked an author's total earnings and compared it to their HP.
I have basically checked the KE ratio before it was even given a name.

It should not be the only metric to judge an author or content by, though.
Sometimes it would be better to only judge the content of the piece, regardless of the author.

Should KE be part of the interface, like on peakd? I think it's not elegant to put it next to an author's name...
I wouldn't have done it that way. It's kind of handy to have quick access to it, though.