Have been trying to use Mobile Me as my cloud storage recently as it integrates with absolutely everything, including Pages/Numbers/ Keynote. I have always used Dropbox until now as it's a far more efficient service, but it was bugging me that I couldn't upload or download directly from Dropbox to the iWork apps. However have found a handy hint on the Dropbox forum- https://dav.dropdav.com. It provides webDAV access to your Dropbox account so you can upload/download directly to and from the iWorks apps. So pleased to have found it and wanted to share it with anyone else who has found this a problem.