That's a good question! There have been a series of cases where a defendant, who has been charged with possession, has argued that through a series of previous judgements, it was determined that the current marijuana laws are unconstitutional. As such, they are able to get off in court. However, in some areas, local PO are still arresting for small possession.
In other places (like the province of British Columbia), marijuana use goes virtually unchecked. In fact, the City of Vancouver made a recommendation to the Federal government that marijuana should be legalized and taxed, or at the very least should be decriminalized.