A few people have asked me this question just this past week. I usually point them to this thread in the forums. Any other suggestions?
The visual data twitter list by @webmuesli is quite a good start to see what’s going on currently:
http://twitter.com/webmuesli/visual-data or for those who don’t tweet, check out the newspaperized format: http://paper.li/webmuesli/visual-data
I highly recommend Stephen Few’s 3 day course. You can find it here: http://www.perceptualedge.com/courses.php
I don’t know of anyplace else you can get so much information around data visualization in such a short period of time.
His books are also great (http://www.perceptualedge.com/library.php) but don’t hold a candle to the courses that he teaches himself.
I would not say it’s a matter of schooling, though if I had to choose something it would be statistics, but it could be any quantitative discipline mixed with some facility with computers.
A better take on it is this post : http://dataspora.com/blog/sexy-data-geeks/
Knowledge of some scripting is essential if you are looking at big datasets, but more important is persistence.
The biggest hurdle is getting data into a form that you can work with. “Real” data sources are often flawed and it takes a lot of work to make sure that you are actually even working with the numbers that you think you are.