I just found out some strange behaviour between arduino and BlinkM. In my setup I use external psu to power the BlinkM MaxM. This power will be triggered via arduino.
The strange thing is... When I start up the arduino, it freezes if a BlinkM is connected via the C&D wire, but doesn't have power. If I disconnect the Clock&Data wire, the blinkm continues running the program like nothing happend (until I cut the power to the blinkm, then arduino freezes again).
I have to remove the Clock AND data wire, removing only one doesn't change a thing.
It took me a while to get here and hope there is some logical explanation for this. I've send an email to BlinkM hopefully they can explain what happens.
See my other thread about my project and code: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1245352480