It's worth mentioning that SC2 has a normal game lobby in addition to the automatic ladder matchmaking. You don't gain or lose rating for playing these games, though.
Also, the matchmaking is based on some form of elo rating. Essentially, you start with some points (1000, I think), you gain points when you win a game, and lose some when you lose. You earn more (or lose less) if your opponent is higher rating than you, and vice versa. Before you begin the normal ladder though, you play in what are essentially qualifier games, to let the system gauge how good you are before tossing you into the ladder.
They've really taken steps to make sure the ladder caters to casual gamers and the less-than-perfect players, instead of just the elite.
Also, the matchmaking is based on some form of elo rating. Essentially, you start with some points (1000, I think), you gain points when you win a game, and lose some when you lose. You earn more (or lose less) if your opponent is higher rating than you, and vice versa. Before you begin the normal ladder though, you play in what are essentially qualifier games, to let the system gauge how good you are before tossing you into the ladder.
They've really taken steps to make sure the ladder caters to casual gamers and the less-than-perfect players, instead of just the elite.