Yes, I include character sheets. I've seen good ones and bad ones, and I've seen good ones put in the wrong place. I'm not a huge fan of character sheets put at the beginning or interspersed early in the story that, well, spoil the story.
However, I find them useful and important when I'm writing nonfiction and I have too big a roster to cover all the players' life stories, and their involvement in the larger story starts in the middle of their lives. I keep it to relevant background information, though, do that only as I introduce the characters, avoid spoiling details that come later, and I don't do that for the super famous people, like the presidents, generals, or admirals, whose relevant background information is already well known.