Do we need to change test documenation to be fit into Agile testing methods?

I'm in the process of re-desigining our test documentation to fit into a more agile development methodology. I'm leaning towards the user of storyboard designs with tests written on the back of cards for each functional element. This seems to be the way to go for me, but I'm interested if anyone has any experience of using this practically on web based projects.

Does it work?
Does it save time?
Does agile testing improve quality rather than standard testing against requirements?