What should I be aware of?

Chatting

Anything which allows users to communicate in conversation with one another – this could be in the form of text-based messaging, voice-based or video-based communication such as via webcam and can either be instant (such as text messaging) or delayed (such as e-mail or voicemail)

Sharing

Anything which allows users to upload data or information (such as pictures, videos, text, location data) that can then be accessed by other users or sent to other users. This includes sharing within a controlled environment (e.g. sharing only with 'friends')

Gaming

Anything which allows users to play games in an online environment against other users. This includes simultaneous play (e.g. an 'online world'), 'turn by turn' play (e.g. chess on a mobile phone app) and play that contributes to a published leaderboard (e.g. console online ranking systems)

Content providing

Anything which allows users to search or browse for content that can either be viewed online or downloaded to their device. This includes information, all types of media and file formats including applications

Networking (closely relates to 'sharing')

Anything which enables users to 'friend' other users, thereby allowing friends to see information about them. This may include the ability to publish content out to a broader audience of users (including friending and building communities.

Shopping and commerce

Anything which allows users to effect transactions on their site, either for physical goods, virtual goods or services. This includes transactions where users pay using 'points' rather than money or where users agree to make a purchase at a later date rather than transact immediately (e.g. click and reserve)