Email widgets can fail to update, lose their assigned accounts and lose the option to switch accounts. The only fix for the first problem is to scroll rapidly down the email list to force an update, the assigned account can usually be reset on the widget, but occasionally the widgets get locked and have to be deleted and regenerated.
Also, not sure if this qualifies as a bug or change in behaviour, but the way audio output is dealt with when bluetooth audio devices disconnect has changed. Whereas in GB, switching off eg. a bluetooth headset would stop any streaming audio, with ICS the audio continues, but is switched to the Note speaker.