I use both and my focus sort of correspond to the PR waves you mention. I use Zumo for less active files and more as storeage although the iTunes sync is nice.

I use both and my focus sort of correspond to the PR waves you mention. I use Zumo for less active files and more as storeage although the iTunes sync is nice. Dropbox is for more active files and sharing web sites in development and such. Perhaps it's the manner I use them but Dropbox seems a little more agile and quick.