Android is not "unstable". The only place where it could be called less than rock solid is the tendency for it to be laggy and to stutter in transitions. This is the result both of insufficiently optimized graphics layer and lack of fine tuning of Dalvik. Interestingly, both are being worked as we speak in Project Butter. And the fast and smooth Jelly Bean being seen on the Nexus 7 is the first fruits of that effort.