In my comment above, I said this is the best tutorial introduction I've seen, even with its few limitations regarding differences between regex implementations.
I completely misread "Handy" as "Hardly" and then saw "Hardly. This does gloss over some of the notable differences . . ." which changed the entire tone of your comment for me.
I found the parent link incredibly useful because it listed common, useful expressions and examples of what you do (or don't) get when you use them.
I don't think of it as a tutorial at all since it wasn't really -- more of a reference or a quick guide.