There is another issue with conditional PR which has created some very tragic situations in the US that have ruined lives.
If the sponsored person is abused by their sponsor in the US, they can complain to officials and retain their PR status even though they haven't lived with their sponsor for the two years. This is a great rule when the abuse is real.
What has (and continues to) happen in the US, is that some sponsored immigrants will falsely claim abuse shortly after arriving in the US because they know about this loop hole. The sponsored immigrant is then allowed to keep their PR status without living with their sponsor for two years. The sponsored person will sometime even end up owning all of the assets (property, bank accounts) that formerly belonged to their sponsor.
The sponsor is then falsely charged with abuse by the police and ends up with a criminal record. In extreme cases where these false charges aren't dropped, sponsors have ended up losing their jobs, their houses/assets, access to chilren from previous relationships, etc.
There are several forums dedicated to false claims of abuse such as these. Some people who have been falsely accused have literally lost everthing and their lives have been permanently destroyed. If you want to read some sad stories, go here:
http://immigrationfraudvictims.freeforums.org/immigration-marriage-fraud-f2.html
I don't think there's a sure-fire way to determine if an abuse accusation is false. So I suspect we will see similar situations in Canada.