Save until it hurts just a little bit, and then a little bit more.

My wife and I did 50% of our nominal takehome every month in a high COL area. It was fine.

The more you save, the faster you get to Stage 4.

If you want to retire earlier than the traditional 65, this is a good starting point to figure out how much to save based on when you want to retire:

http://www.mrmoneymustache.com/2012/01/13/the-shockingly-sim...

10% is a pretty common percentage and what I put towards bonds and stocks each month. I do pretty much what the parent post said.