The following comments are something I just posted on the Author's forum of SpeakerSite.com, and I think they deserve to be posted here, too.
I just got asked a very good question, about how one balances life and writing a book. We have businesses, families, spouses, and kids to deal with, so how does writing a book fit all of that? I wanted to mention this here both to spark discussion and because this may be helpful for people.
Writing books is a pest and it rarely pays off really for the time you spend. Compared to what I make doing independent consulting, contract writing, or writing magazine articles, books don't pay nearly as well for the time it takes to write them. Nevertheless, we do it because there's always that chance that that particular book will pay off handsomely and also because it's just one of those Things We Should Do. I also recommend it to everyone because your writing and planning skills improve enormously after doing even a book or two.
I haven't come up with a great balance to the process, myself. I wrote my first 15 books from 1987 to 1995, when I was in a marriage I didn't enjoy, so part of it was my way of keeping myself away from my then-wife. I was younger, too, so I had more energy and was able to skimp on sleep and survive in the short-term. (I ended up a Type II diabetic as a result of years and years of sleep deprivation, so don't do this yourself.)
In terms of finding balance in your own lives--assuming you do a lot of this--you might want to view writing a book as that extra 10-15 hours/week that we all need to do in self-marketing to keep the pumps primed. I would also strongly recommend not doing books (a) back to back or (b) simultaneously. Back to back will exhaust you and I've never done well writing two books simultaneously because I keep having to jerk myself out of one creative reverie and into another. I didn't like it and I ended up spending too much time in the transition and my writing speed went down.
The bottom line, though, is that this will take a lot of time and you need to be ready for it. I was talking to my current editor at Wiley the other day, who was saying the the Editorial Committee has this image of authors lounging around all the time. (He doesn't believe that himself, but the EC does, apparently.) "Ha!" I said, "I always tell my writing students that as an author you can work any 12 hours a day you like." He liked that one a lot. It's true, too.
BTW, I recently posted an article about those last few weeks when you're finishing a book. It equates being in prison with the writing process, but not in any way you'd expect from the sound of it.