Idea: Blizzard frequently puts a newbie on my team that was far below my enemy average MMR, he got crushed and we lost the game.
Chart:
http://i.imgur.com/k07vwMx.png
This graphs win rate over the difference between a teams lowest member MMR and their opponents average MMR (Team MMR).
My Thoughts: This significantly impacts your win rate. If your lowest MMR team member is 500 less than the enemy average, your win rate is 48%. If it is 1000 less than your enemy average, your win rate is 41%. Thankfully differences greater than 1000 aren't too frequent.