I grabbed two of those 36 key keypad boards from Paul at the last dork bot, he grabbed them out of those POS boxes [with the big LCDs that he has posted info about]. I wanted to get them working with the Benito and also wanted work with i2c a little [as I have a bunch of these 8bit i2c i/o expanders]. The keypad has 20 i/o pins so the Benito cannot use it directly anyways.. though 12 bits of shift registering would probably be better... but either way, I wanted to use what I had + i2c.
I've posted some of the code I've been using for midi on an avr chip [atmega16]. It should work on other avr chips with little or no modification. I'd love it if others would test it out and and contribute.
I've included a little bit of info and some example code here: http://x37v.info/projects/microcontroller/avr-midi/