I have only just got round to finishing my MIDI Accordion project today.
The accordion is powered by an Arduino Mega which polls a 16x3 PTM switch matrix used to create the array of note keys as well as a few other switched and potentiometers for some other functionality, i.e. changing MIDI channel, velocity, pitch bend and modulation.
And here is a video giving a little more detail about the project:
I also have a couple of projects lined up for summer, one is a scalable home automation system with a web UI and Android application, for this I am currently working on an RF networked Arduino which can be produced as cheaply as possible, use as few components as possible and use as little power as possible (particularly as I would like them to run on a 9V battery for months).