The Dropbox support in the iPad app is a nice feature but obviously of little use if you do not use Dropbox! Please consider adding some of the other major cloud services, e.g.
* Google Drive
* iCloud (not really the same thing, but it would be awesome if Endnote on a Mac and the iPad used iCloud as a more seamless backend in some way).
Also, and arguably more important, WebDAV support would enable a wide range of serivices, including university ones, cloud companies with WebDAV enabled (e.g. CloudMe and Cubby), and so on.