In libs/Zend/Registry.php (line 146), replace:
(This is fixed in later versions of ZF.)
fixed in 
vipsoft, do you know of any blocker to update all the zend files used in Piwik?
btw as a side note, I am thinking of migrating to use Zend_Form later.
With respect to #497 ? I haven't done the analysis yet on patches (eg which, if any, must be forward ported).