From Social Patterns
Microblogging allows users to create short posts. These are often aggregated into a stream (see Activity Streams) and can consist of text, pictures or video.
Services like Twitter and Yammer (for Enterprise) constrain users to 140 characters. People’s posts flow into the stream based on time and have amore ephemeral nature than blogging. Most people use microblogging to alert others to what they are doing at that moment or to ask short questions or announce whereabouts.
Ecosystems of other functionality have sprung up around the microblogging phenomenon which allows users to aggregate their own posts onto their blog sites, search for specific threads of conversations, post onto other services (twitter posts appearing in Facebook) and group people together around specific topics of conversation.
Use as a light alternative to blogging.
Use when you want to allow conversations and real time updates but don’t need synchronous conversations like Instant Messaging.
The basic interface for microblogging is a text field, with clearly marked character count limit and a submit button. For alternative to text (video, photos) clearly indicate size and time limits.
Provide a method for viewing once posted. Both an author view and a community view should be available.
Sometimes all you need is to say a few words or share a short thought. Microblogging addresses that need without the heavy duty interface or overhead of blogs.