I actually disagree with Rockridge. The fact is that I've trained people from all over the world who have "learned by the seat of their pants" and invariably, the simplest of operations that can make things so much easier in the long run has eluded them to the point that they went seeking training. Obviously that's not true for every person, but it is for the vast majority.
I COMPLETELY agree with Jeremy's assessment. Pro Tools is a tool originally designed around an engineer's toolbox. Now it has more features that make it helpful in the creative side, but the basics of the system can still be more easily understood with a good engineering foundation. It does work the other way too, ie. Pro Tools to help learn engineering, but it's not the best way...in my opinion, of course.
Also, Digidesign just released
The Pro Tools 101, Official Courseware book. That's a pretty good place to start!