Some readers asked about career choices in visualization recently, and I was about to write a response until I remembered I already did in 2008. A few group names changed and examples in some areas are easier to come by, but most of it is still valid.
You still find a lot of jobs in journalism, business-related analytics, at design studios, research labs (academic and industry), and freelance. It seems like there are more opportunities now than there were then. There are also a lot more tech-related jobs now. In 2008, Twitter hadn't quite hit mainstream yet and most parents weren't on Facebook, whereas now, web companies sit on more data than they can interpret.
There are visualization jobs pretty much wherever there is data. Which is practically everywhere.
That said, there's also more competition for these jobs, and high school science fair Microsoft Excel experience probably won't be enough to get you the job you want.
So one more important addition to the 2008 post: Learn statistics. It still surprises me how little statistics visualization people know (generally speaking of course). Look at job listings though, and most employers list it in the required skill set, so it's a big plus for you hiring-wise.