Hey Ribble
There's a long time argument on the forums that MM makes games more difficult for players over a number of games. The idea behind this is that MM looks at the skill of the players on the teams and puts higher-skilled players on the opposing team to make it harder for you to win.
There are other players who have read before that MM does NOT analyze player skill, but may in fact place you as low-tier to offer you a greater challenge in a certain percentage of games that you play. In this scenario, MM remembers how often you are low tier / high tier and manipulates how often you are low or high tier.
Finally, there's those who believe that MM is entirely random, and that MM simply grabs you and your tank to make up the team needed at that very millisecond that MM starts building teams for the next match for which you're available.
Who's right, and who's buying the other guys a beer? If you can answer this question, I will heartily thank you!