To much to write here, but I'll try to name few:
- NAME - easy to remember, good domain, suggestive accordingly with your intentions.
- UI/UX - to be attractive and same time simple but functional, adaptive and responsive to user's needs.
- CLARITY - in this way the users to understood in few clicks how it works and what could take advantages from your network.
- CUSTOMIZATION - to give the users a relative control over the interface and modules (to change the theme, to drag the modules in different places, to add/remove modules, etc).
- CLOUD PROVIDER - a good provider which to offer scalability and speed
- SPACE (optional but already become a must) - to provide to your customers cloud storage which to integrates with the main functionality of your network.
- COMPARTMENTALIZATION - as to provide users the possibility to create groups(circles/tribes/etc), to assign different functions to groups/files, to create behavioral rules for files/actions/etc
Depends on you how complex want/need this network to be.
If you consider I could help you draft the architecture of this network, you may reach me at bogdins at gmail dot com or by skype at technobogdins.