How safe is IE8's InPrivate?

I was going to email NFiH (I hope you don't mind) about this, but decided to post here so regular posters as well as lurkers can read it. I'm sure there are people who are using this option to view this site on the assumption that no one can know they were there. So, how safe is it? What methods does it use to remove the tracks? Has anyone tried to retrieve them successfully? How does it compare to other browsers, such as FireFox? Sincerely, Shaper of Worlds We are the music makers, And we are the dreamer of dreams, Wandering by lone sea-breakers, And sitting by desolate streams; World-losers and world-forsakers, On whom the pale moon gleams: Yet we are the movers and shakers Of the world for ever, it seems. --Arthur O'Shaughnessy