There is a widespread belief that more often than not the assessment
values are not correct and the errors are usually not in favour of the
homeowner.
Here are some reference URL's for some insight into the system.
Ontario's Municipal Property Tax Assessment System
(Authored by E. J. (Ted) Legg - October 2005)
http://www.fsnaottawa.com/branch_pdf/tedlegg.pdf
The MINISTRY OF FINANCE is responsible for the Assessment Act and
regulations.
http://www.arb.gov.on.ca/english/content/propertyassessment.htm
Resolving Assessment Concerns
http://www.mpac.ca/
Poll results can be see at this URL
http://www.sesresearch.com/library/polls/POLONT-F05-T162.pdf