Students should use citations to Wikipedia with caution. Some academics and teachers believe that Wikipedia is not a reliable source of information source and may 'force' their values on others resulting in low or fail marks being given to work supported by citations from this source. In some institutions consideration is being given to blocking student access to this information source.
A brief search of the Internet will provide many examples of where articles in Wikipedia have been altered to include erroneous information or have been written to influence the views of others using false information.
Hence students must use Wikipedia with caution and under no circumstances should it be the only citation used to justify an argument, stance or view; it is not reliable enough to be used in this way. In situations like this students would have little defence to criticism and possible academic consequences. However Wikipedia does have many strengths, not least the facility to discuss and 'correct' articles and its open source nature means that it is freely available to users.
In many institutions and journals, you are not permitted to include references that are not subject to authentication in the formal list of literature cited; Email and other personal communications belong to this category. Instead these are mentioned in the text e.g. Tribles have a very high reproductive capacity (J.T. Kirk, personal communication, June 12, 1989).
For more information on referencing using the Harvard style please see the article "Harvard style bibliographies and references" published by the University of Leeds. The site's Writing Research Reports and Dissertations Links page contains a section on writing research reports that may also be useful to readers.