So a buddy and I have been playing 2v2 at the moment, and doing pretty well. We're still in bronze, but we're at about 100/100 win/loss, give or take. We've been top 5 in our division for a few weeks/months now, and can't get promoted. But every so often, we're getting matched against a team with 2 platinums, and naturally getting raped. 
 
Can anyone shed light on this?

As you get higher, the game pits you against people in higher leagues.  Usually when it's preparing to bump you up a league.  Back when I played, I was in Gold, but after 2 weeks or so, 4 out of 5 games were against Platinum opponents.  After a week or two of that, it bumped me up to Plat. 

It's random fights, and it just goes on your W/L ratio. 

" It's random fights, and it just goes on your W/L ratio.  "

" @KaosAngel said:

" It's random fights, and it just goes on your W/L ratio.  "

How does that work then? If we're bronze, surely we should fight bronze, not platinums? "

" @Fallen189: It's how it's been since the beta and retail.  It's always a random guy from any division, but they try to push in someone from your same skill.  That's how they determine the "favored to win".   "

" @Fallen189 said:

" @KaosAngel said:

" It's random fights, and it just goes on your W/L ratio.  "

How does that work then? If we're bronze, surely we should fight bronze, not platinums? "

It has to do with your win/loss streaks as well.  Its pretty possible that you guys have won the last 5 games in a row while the platinum guys lost their last 5 or 10, including gold and silver guys. "

it sucks thats about it. i have played against gold players repeatedly and im only in bronze. sure i only lose like 8 points when i lose but its annoying as hell

Long answer: 
http://www.teamliquid.net/forum/viewmessage.php?topic_id=142211

 Short answer: 
 It happens, sometimes the system matches you up against higher league players to determine whether you're ready to advance to the next league. Considering you keep losing those games, you're probably not ready yet.

I was under the impression that it pitted you against higher skilled players if it was determining if you were ready to rank up. If your w/l ration is 50/50, then it puts you through a sort of test by matching you up against someone of higher rank than you. If you beat them and several other tests afterwards, then you get promoted. That's how a lot of my promotions have happened. I'm currently being pitted against a lot of diamonds and plats in both my gold league 4v4 and 3v3 so I'd assume I'm going through a test as well. The weird thing about it though is that alot of these tests have also teamed me up with bronze players so it'll be me in a team of bronzes versus a team of plats and diamonds. Naturally, we get stomped....badly....as in take our own expos during fights just to taunt us badly.

Who you are matched against is based on your MMR (google it or check out Thule's TL link, it's kinda complex.  I read a bunch on this stuff out of curiosity a while back).  Your MMR raises and lowers based on not only how much you win, but who you win against.  The better the player you beat, the more your MMR raises.  The worse the player you lose to, the more your MMR falls.  As previously mentioned, when you are nearing promotion (as I currently seem to be as I am playing almost exclusively golds and platinums and I'm only silver), you typically get matched against players in higher leagues who, typically, but not always, have a higher MMR.  The more you win against higher MMR people, the better the people you face.  Keep in mind that if the system cannot find an ideal match it will keep looking until it finds a close one (close being a somewhat loose term in this case). Hence why sometime you get matched with someone much better or worse than yourself.

This is how it works. in SC2 there are two placements every player has. One placement is the whole bronze-diamond league, and the other is a hidden score that no one can see. Your hidden score is actually what matches you up with people. Theres a thread about this exact subject over at the battle.net forums explained by the blizz dudes.