Polls are a convenient way of gauging opinions of participants in a course or learning community, and polling tools are often included in learning management systems. They are also often part of software and web services for collaborative work.
Jim Klaas and Jon Baggeley (2003) have compiled a useful overview of how polling (questionnaires, quizzes, surveys, assessment products, etc.) are used in online learning. There is a link at the bottom of the article to the Athabasca University software evaluation site where evaluations of individual polling programs can be found.