Thanks to Mad Hatter for creating this space and inviting me to post, and apologies for the tardiness of this introduction! My "alternative career" is in management consulting, although I'm currently on an extended maternity leave spending time with my 4-month old daughter. (My time on the computer has decreased markedly, but I am following the conversation with interest!)
I have actually had two alternative science careers: I first took some time off between college and graduate school and found work with a small science publishing company. Because of the small size of the company and my relationship with one of their authors, I was able to contribute to editing the scientific content of a textbook and had a fantastic time. However, I realized that publishing was less appealing to me than writing books, so I packed my bags and headed for graduate school.
When I began graduate school (in physical chemistry), my long-term goal was to become a small liberal-arts college professor, teach classes, run a small research program, and possibly write my own books someday. I did not find graduate school inspiring, and by the time I was halfway through graduate school I had decided that I wasn't committed enough to the tenure track (and the odds that Pablo has illustrated) to uproot my significant other and dedicate the next decade of my life to getting tenure.
Several friends suggested management consulting to me as a career, so although I was skeptical, I looked into it. I accepted a job offer from a management consulting firm and I've spent the last two years in a variety of locations, working for a range of companies with different focuses. I don't know how the next year will unfold now that my daughter is added to the mix, but I have thoroughly enjoyed my time in management consulting and think it was a fantastic move for me.
One important thing to consider when thinking about career moves is what truly motivates you, and what brought you to science in the first place. In my case, I loved thinking about science, solving problems, creating hypotheses to test in lab, and teaching others about science; however, I was not fond of benchwork and the rigorous trouble-shooting required to get experiments going. The tasks that energize you in the lab can be great clues as you venture into the alternative career realm (and save you from alternative careers that don't really suit you).