I don't use Numbers or QuickOffice, but from what I understand, the only way to sync files to the iPad to use with Numbers is to plug it into your computer and sync with iTunes. Whereas, with QuickOffice (and maybe others) you can sync over wi-fi or 3G with Dropbox. Something to consider. Of course, when iOS 5 comes out with all of that fancy "cloud" technology, this point may become moot.