When I was a graduate student I was convinced that I was learning absolutely nothing. The biggest reason I quit was my concern over the opportunity costs of staying since I didn't feel my program offered me any relevant real world skills. Being able to read a methods section, debate the epistemological underpinnings of the social sciences, and embrace a construct and theory did not seem like particularly relevant life skills.
Yet as I entered my first job after quitting graduate school I was amazed at not only how much I had learned, but what I had learned. The most valuable lessons are not the take-aways that I or even my advisor and committee members envisioned.
1) Teaching is management experience. If you have run research team or TAed you know how to explain assignments, break them down into manageable pieces that are appropriate for the skill levels of your staff, and hold people accountable. As a manager, you are uniquely suited to developing your team's writing skills, giving constructive feedback, and providing training and development. You can also schedule out projects and calendar them, and work backward to determine due dates and start dates. Handling sensitive information, and identifying the kinds of problems HR wants managers to be aware of (sexual harassment, conflict of interest, etc.) is second nature.
2) Public speaking. You can present concepts and explain them, provide context and point out limitations and nuances. All that teaching has totally prepared you for anything, including filling time in front of an audience. You can answer questions and think on your feet.
2) Mad (and super fast writing skills). Research and churn out thorough, concise memos faster than any of your coworkers. Just don't work too fast or they will dump a lot more work on you ;)
3) A high tolerance for stress. Seriously, you have juggled teaching, research, publications, grading and coursework, all while trying to make it on 16-20k a year.
4) An even higher tolerance for crazy. No one does neurotic like academia, but be warned that the workforce is full of crazy people.
5) No concept of what it means to have a weekend or weeknight free. Working long hours isn't unusual, so you will have the stamina and pride of work to put in the extra effort when you need to, and with most jobs the new found freedom of not taking work home all the time is awesome. Even jobs with long hours will seem great by comparison to your old life.
6) A low paying job probably doesn't pay as badly as being a graduate student. Seriously, employment law makes it very hard for you to find something lower paying than being a graduate student.
Of course, some of your skills may hold the potential to cause problems.
7) The ability to critique and destroy just about everything can really piss of your coworkers. Academia trains us to debate and spar verbally in a way that may be extremely inappropriate depending on your work place, so be careful with this one.
8) Theory and past experience in initiating, planning, and scheduling projects can help you predict when something your organization is doing is going to go terribly wrong. You can warn them, but your coworkers likely won't listen. They really don't care about or understand the role of vigilance in decision making, the risks of group think, or how bona fide groups may suggest their initiative is going to fail spectacularly.
9) Face time and Freedom. You are going to hate not being able to set your own schedule, and decide which ideas and projects you want to pursue. Being indoors all day also makes you really miss the sun.
For me the hardest part of leaving graduate school was trying to silence my inner know-it-all, and adjusting to an environment in which not everyone was aggressively analyzing everything all the time. My managers in my first job had a hard time managing me because they didn't have much feedback to give me. They had never manager or taught, and they were frankly in over their head, Being in the workplace after graduate school sometimes felt like my undergraduates were running the joint, but with no one around to point out what they were doing wrong.
Look for strong, experienced managers and mentors who you can learn from. I lucked out in my current job--I'm actually working for another former graduate student who quit just like I did many years ago.