Systers just started a 'best of' blog that highlights useful conversations that have happened on the popular mailing list for technical women. The first post, Life as a Professor, is all about what being a professor is like, particularly in the work-life balance sense.
I find the responses either depressing or encouraging. One thing's for sure: it's not a 9-5 job. As one person said,"It’s a huge part of your life even when you aren’t in the classroom or lab." Whether that's good or bad depends on the individual (after all, I'm always thinking about teaching, learning, and outreach, so if you love what you do you may not want to leave it completely at work).
For me, the words of wisdom in that post solidify that I would be much happier as an instructor without the added pressure of running a research lab. Plus, if I don't want to be a professor, I can skip that whole post-doc phase, which suits me just fine.
Do check out the post if you are at all considering an academic career.