In the game where I was teamed up with my clan mates rather than randomly, my elo was in the 1400-1500's. When the "season" was over, the team would be randomly created. My elo suddenly went up to high 1700's, my skills however remained the same. I'm not the only one to whom this happened, many people criticized the elo ranking system for that particular game due to this and totally unbalanced games where one could guess the outcome of the game from start even regardless of what the elo had to say. The same would apply even when the teams would be randomly balanced. In that particular game economy (think of a starcraft-like one's) is shared. If you have a noob in your team and he's wasting all the economy on useless stuff, even the best player can't do much to win the game.
I disagree with this. I would say your elo deserved to be in the 1400s-1500s because your team was presumably not as good as the teams you were randomly matched with.
Starcraft does this correctly IMO because you have a ranking for every team you play with, as well as a "Random Team" ranking. Sure, if you play by yourself you'll get crappy players but your ranking is accurate on average.
Halo Reach broke off from this type of ranking system from the previous games in the series, and it was part of the reason that I stopped playing. They had some sort of voodoo to figure out how well you as an individual did in a team game. Winning was no longer the objective in team games, because it was no guarantee that your rank would increase. To rank up, you basically needed a lot of kills, which took a lot of the strategy out of the game since everyone went into run and gun mode most of the time.