One feature I like about symfony is the ability to use each component independantly of the entire framework, It's just a case of downloading the library and using straight away.

I have been looking at PHPUnit and symfony's own "lime" unit tester and although PHPUnit is good, I'm prefering the lime as it is easier to read (and even better with the lime extra plugin).

With the component base of symfony you can also use lime in non-symfony based projects. So I can use the same unit testing framework for all my projects.

This is another plus for symfony. Some components are available at symfony components.