Though unified, one of the cool things about the Zend Framework is that you can just pick and choose what components you want to use – you don’t have to buy the whole cake to take advantage of all that juicy object oriented PHP code.
With the Pear framework, it is more of a hodgepodge/motley of assorted components. Pear is widely used (and useful) but it does cross over (in terms of functionality) with what we have in the Zend Framework.