Beta 8 seems to be uncompatible with Python-launcher :

If Canola doesn't start after upgrade, this may be one possible cause...

EDIT : on one tablet (N800), removing python-launcher was enough to get beta8 up and running.
On another (N810) beta8 still fails with the same message adammelancon reported :
IOError: [Errno 2] No such file or directory: '/usr/share/canola/plugins/plugins.pickle'

(both use OS2008 and ran beta7 just fine).