An article on hrmonline.ca talks about the risk of giving references: Reference risk: could ex-employees sue? It seems that in the UK, ex employees have successfully sued their former employers for giving bad references. It has not happened yet in Canada, but it could happen.
If you give a bad, yet truthful reference, the ex employee may come after you due to the fact you have impacted his/her livelihood, claiming libel. If you give a decent, yet untruthful reference, your company may be liable for damages resulting from hiring that employee.
There does seem to be an understanding amongst HR types that if someone will only confirm dates of employment and job title, this is code for "I would love to say more but it is all negative so let's move along". I would be lying if I said I have never resorted to this. Other options are to employ CourtRoom Rules. Only answer the question you have been asked. It is a sad fact that reference checking is not taken as seriously as it should and often the person checking the references has not even met the candidate. They are simply going down the list of questions that they have been provided. If this is the case, then just answering the questions is a pretty good way to remain neutral without getting into hot water.