I've just gotten out of the Practice League so maybe there is an option later on to select opponents.. But I was wondering, how does SCII select an opponent? I imagine its pretty region-specific as it would take latency into account - as I could swear based on some of the questions I see on here it harder in my region (Asia-Pacific)...
The Starcraft II match making system picks players from your region that have similar skill. It maintains a hidden skill number which it uses to match you against other players, and adjusts this number based on the skill number of the opponents you win and lose to. It also does it best to make sure you have a 50% win-loss ratio.