In the mid-90's I met a guy named Tim Anderson who had built a painting machine and was controlling it with Max running on a Mac. (check out Tim's recent homemade wooden hydrofoil video - and his Robot Art video). He explained that Max was was a new kind of intelligent music software for sending MIDI, but it could control anything, really. Soon my plans for the Sound Square included the idea of sending the gesture output thru Max for processing before playing it audibly.
Around the same time I read a book called Interactive Music Systems, written by a guy named Robert Rowe (then at MIT, now at NYU Steinhardt School). He had built (and includes on CD) a Max patch called Cypher, which consisted of two horizontal rows of objects. The top row were "listener" objects, and the bottom row were "player" objects; you programmed them then patched them together... just like all this "new" stuff where you build synths and stuff inside a GUI. (I recently tried to read the disc but my XP machine spit it out and my Mac Powerbook wasn't quite sure what to with it, either.)
So really Max is the Grand-Mac-Daddy of them all. Somewhere along the way the product became commercial and is now sold and updated by Cycling 74 along with some other cool stuff like Jitter (for video). Interesting recent news is that Abelton, makers of Live, and Cycling 74 are getting hitched in some sort of merger. A great feature of Max is the huge community and tons of existing patches, and Live has a rabid following... Could mean great things for both products or the beginning of the War for Middle Earth.
I've been running through the tutorials that come with the 30-day eval copy and they are short and easy to get through, and definitely get you past the "duh" factor and up and running.
I'm only up to chapter 8 so far - there are a total of 53 chapters... yawn.