I've written a tutorial on the communication between Pd and Arduino, aimed at Pd users who want to program Arduino without using the Firmata firmware.
You can get it here http://drymonitis.me/code/ (look for the specific link).
The .zip file contains the tutorial .pdf, all Arduino sketches, Pd patches, as well as Fritzing files of the circuits.
The tutorial is split in ten projects which are the following:
1 - digital output
2 - digital input
3 - analog input
4 - analog output
5 - analog and digital output
6 - more than one analog inputs
7 - servo motors
8 - analog and digital input
9 - multiplexing
10a - output shift registers
10b - input shift registers

Feedback is welcome : )

I've just made some corrections to the Servo motors project. You can get the tutorial from the same link.

Thank you!

I was blown away when my friend Tom presented this to me before the PD weekend in San Diego via new blankets. Very interesting we are both working on relative things and its super important for streamlining new development protocols for PD and libPD. If you have time please check out the patches I've been working on.

https://github.com/cskonopka/arduivis

Instead of going the project route, I decided to create models of communication so it is easier to modularize the concepts into user patches. I still need to fix up/test some things but the idea is coming together. Also I figured out a way to stream the serial data without ever using if(Serial.availble()). Thought you may dig it.

Thanks for all the amazing work! It would be great to chat sometime

Just corrected some more stuff, hope this is the final version. Links are the same.
Enjoy..

My website is down for some time now, so if anyone wants to download the tutorial, go here http://patchingcircleathens.labyrinthos.gr/arduino-for-pders/

I've moved my website to another server and got a new domain (it's Superglue home server, for anyone interested), so all code and tutorials I've written (including the Arduino tutorial) are now here http://drymonitis.spgl.cc/code.html