TaskRabbit won't disclose specific revenue per task, but says its average service fee is 15%, paid by the person posting the job.

WSJ: Websites Let People Farm Out Chores

Many of these are free, although US firm Sensei Project Solutions is among the first to charge a fee, for its "task analyser", which is designed to identify problems or missing information in users' documents.

BBC: Microsoft launches Office 2013 software suite