Micro-blogging is a form of blogging where immediacy, rather than substance, is key and content can be authored and published anywhere by using a mobile phone, web browser, or other device.
Twitter is the best known micro-blogging service and is crossing over into mainstream culture, being used for corporate communication, emergency alerts, and even church service. The strangest use I've seen yet, however, has to be Twitter Taste Live, an on-line gathering where folks around the world, who have purchased the same types of wine beforehand, chat using Twitter, sharing their opinions of the wines and asking the winemakers questions.
Twitter's success has not come without struggle. The growing popularity of Twitter has created occasional virtual traffic jams in which Twitter has had to temporarily shut down various parts of their service and display the infamous fail whale. The video below lampoons the tantrums some users have directed towards Twitter, and its administrators, during downtime.