The new rMBP is about five hours if you don't touch it at all. under 4 hours if used for working. It is a step down from my previous 2012 model which is a damn shame.
Sure I can. I generally have the screen turned down quite low regardless and if I know I’m going to be without power I’ll close unnecessary programs, but I can do a bunch of web development with Sublime and a browser going for a full 7-8 hours.