Using the new corelib it appears that the I2C bus looses connection to the device intermittently and eventually just hangs the board.
I attached a HMC5883L to the I2C pins and it appears to recognize that the device, however, when I run a simple sketch to get the magnetometer readings they are inconsistent. Sometimes it appears reasonable values are out and then values may change from something on the order of 440 to 65236 which is not quite right :). Then after a minute the board hangs.
I immediately attached the 5883L to the Mega 2560 and ran the same sketch and guess what - it worked fine, no problems.
Based on reading other board forums it appears that the Wire library is probably not behaving as it should.
This needs to fixed asap as the I2C bus is critical to a lot of applications that people use. I do know that there is an open issue that has been identified as a bug but it may go deeper based on the problems I am seeing.
I can not do any further testing as I do not have a scope.
Regards
Mike 