W3C HTML 4.01 Recommendation on the usage of appropriate GET and POST:
The "get" method should be used when the form is idempotent (i.e., causes no side-effects). Many database searches have no visible side-effects and make ideal applications for the "get" method.
If the service associated with the processing of a form causes side effects (for example, if the form modifies a database or subscription to a service), the "post" method should be used.
Note: The "get" method restricts form data set values to ASCII characters. Only the "post" method (with enctype="multipart/form-data") is specified to cover the entire [ISO10646] character set.