boybokeh
It's a great environment and if you check out openprocessing.org you will find all kinds of very cool examples. The latest version of processing has 3 modes: standard, javascript, and android. The main limitation of the javascript mode, presently, is that community libraries will not work.
This is what killed my little engine. I based it around a community built physics library called fisica (and was more or less a wrapper for box2D) but last I checked it had not been updated to work in javascript mode, thus limited the export options to applets or .exe.
I've a project this fall building a musical tangible user interface for autistic children and will be doing this in processing as I need to program a micro-controller (arduino). Working with sensors and actuators is not really something you can practically or easily do at this point in C2 but maybe one day. Security limitations within html5 specs make things difficult when developing these kinds of applications.
Seems there is always a trade off between accessibility and functionality. It's understandable because the more access you have, the more damage you can do. Being able to develop applications that work on multiple operating systems and multiple devices without separate compiles, is a beautiful thing but there will always be a trade-off.