I'll be a father in a couple of weeks but I've been working on a "life/work balance" for quite a while now. If it ever comes up with a client I remind them that we're running a marathon, not a sprint, and that putting in a solid 8 (or 9), consistently, week in and week out can get a tremendous amount of work done. It's really easy to work too much and burn out, even if you have a lot of experience -- and 40 hours per week is a huge amount of time if you're making every hour count.

Kudos for making extra time for your kids. I plan on doing the same.