Let us just cut through all the spin both sides are putting out there. There is only one basic difference between the mixed member proportional (MMP) system and the existing first-past-the-post system. Surprised? Well you shouldn't be. The MMP is "mixed" because 90 of the seats are going to use the exact same first-past-the-post system we already have in place for 107 seats. The difference is for the balance of the seats, which due to a larger legislature with the MMP system will be another 39 seats.
Parties that receive at least three percent of the vote in Ontario will be guaranteed a seat in the legislature with MMP. If a party wins a smaller percentage of the 90 local seats than their percentage of the vote then they will get additional seats from the 39 "list" seats. The Members that will hold those seats will be determined by each political party, while the Members holding the local seats will be elected by the local voters.
So the debate about the first-past-the-post system is not as relevant as some might have you believe. In the current system 107 seats will be determined that way. In the proposed system 90 seats will be determined that way.
The real debate in this referendum is whether the addition of 39 "list" seats, and the Members of Provincial Parliament selected by the parties to fill those seats, will improve our democracy or not. Some say voters will have more choice and the legislature will better reflect the public, and will therefore be better. Some say fringe parties will certainly be elected and that it is not good for democracy to have politicians choosing 30% of the MPPs.