It occurred to me that people who haven't been grouping or raiding a lot don't know what role various classes have in a raid, or of class design in general. You can go read the page on the worldofwarcraft website, but they make every class sound equally great at everything. That's just not the reality of it. So I can keep complaining about how many people get stuck between little knowledge and expanded knowledge, or I can take my shot at fixing it via explanation.
If you don't know how a particular character or spec of a character fits into the group game that follows the leveling game, this is for you.
It's possible to find out everything I'm about to write from various places online, but as far as I know, there's not one place where it's all connected. Most articles are written from the point of view of one class or another; every guide is written by that class, for that class.
This is going to be the top level view, how raid leaders (and possibly Blizzard designers) look at classes and their role in the game.