I had access to the Kindle lending program for two months and none of the books available interested me. Maybe it depends on the genre, but the one that interests me had mostly self-published books, whose price multiplied by 12 would have been less than the Prime membership fee.
I now borrow from libraries, and it's fantastic. I think I died and went to heaven when I finally discovered eborrowing - if Overdrive were a man, I'd want to marry him and have his babies!!