What's a postdoc? 90% of the time, that's the next question I'm asked after people ask me what I do for a living. Or worse, people who know I spent 5 and a half years in grad school will say "wow, I can't believe you're still a student!" It's clear that most people outside the scientific community don't know what postdocs are - Students? Interns? Trainees?
People should know what postdocs are - at very least so that they don't call them students! More importantly, the public should know who is actually doing the vast majority of the experiments and fieldwork that get published in hundreds of scientific journals every week: postdoctoral fellows and grad students. They are the people who pick up the test tubes and pipettes, go the lab bench, and run the experiments. That's not to say that the professor just sits back and gets all the credit - professors are generally full intellectual participants in the research, and they're usually the ones who came up with the main idea for the research project. However, the point here is that grad students and postdocs aren't simply trainees learning their trade; they are practicing scientists who produce valuable, tangible work. Unlike undergraduate education, this is on-the-job training much like any other career field.
Postdocs are no longer students - they have their PhDs, and they're not attending classes, taking tests, or writing a thesis. If a graduate student is an apprentice, a postdoc is a journeyman - a credentialed, capable scientist who is gaining more experience under the guidance of a senior scientist. A postdoctoral position is a chance to learn some new skills and work more independently without having to jump through the administrative hoops of grad school. The research you do as a postdoc lays the foundation for what you'll do in your own lab as a professor.
I still seem like a student to my friends in other careers because my job as a postdoc is only temporary (3-5 years), and I still make well below the median US income. (Starting postdoc salaries range from $30k to ~$40k, and rise to $40-$45k after 2 years of experience.) This is why the career path of an academic scientist seems so long - you hardly earn anything and don't settle down until you're in your mid- to late 30's, even though you have a doctorate and you do demanding, highly technical work. You spend 5+ years as a grad student with a 22k annual salary, no retirement benefits, and bare-bones health insurance. Your reward for earning a PhD? A temporary job with a low salary, no retirement benefits, and if you're lucky, decent health insurance. All this, while your friends who went to law school finished their degrees years ago, got paid $50-60k during a brief clerkship, and are now raking in more money than you'll make as a tenured scientist.
On the other hand, if you work with a good mentor, you wouldn't trade this job for any other. In spite of the unsustainable pay level (you'll never retire or send your kids to college on it), as a science postdoc you get to continually drive your intellect and creativity, you get to play with fun, high-tech toys, and you have a degree of independence that almost rivals that of a freelance writer.