Dark Age Ahead
For those who don't know anything about sampling, the problem with making the long form of the census optional is that the results will be biased to overrepresent the sorts of people more likely to complete the census form, and underrepresent the sorts of people who are less likely to complete the form. This may not sound like a big deal, but it is. The census data is some of the best, most fundamental data available for all sorts of important analysis and research done in all areas of life (setting electoral boundaries, municipal planning for roads and schools, analysis of the impact of economic policies, etc. etc.)
Credit to Stephen Gordon for initially bringing this to my attention.
The Pundit's Guide has an excellent summary of some of the uses of the census data in Canadian Elections here.
It's depressing to have this great country governed by morons, especially when they received less than 40% of the votes in the last election.