i have seen many people using joomla as framework for application development but
i think cakephp will overcome joomla as they have different mission,vision and structure.....
plus i feel joomla is not generic(compatible) in the sense that it tends to develop every thing of its own.
A full php developer finds himself to be only half joomla developer and need to learn its structure,convention and all
where as with cakephp,if you know MVC or even codeigniter,you know more than 50% of cakephp
and it has many features like baking and all....
so as other said it is not ideal to compare both
but if compared
i vote is for cakephp