Oh, and one more thing; I love what TLO says at the very beginning about balance. I love his perspective on it.
I've been thinking about balance recently in the context of StarCraft II, and let me say something that may rock your world: StarCraft II is the most imbalanced game ever.
Ok, first of all, back to what TLO said. He said that it's not imbalanced if you can counter it or out-play it, and regarding the Terran mech build (which TLO and Day9 discuss) it can easily be countered.
Back to my comment on balance. Seriously, StarCraft II is incredibly imbalanced. But, it is sooo imbalanced that everything just works out in the end. I was going to make this really long post about my thoughts on this, but I guess I'll just leave it at that. I mean, it's mostly self-explanatory (I think).
Think of it this way: every unit in the game is very powerful. There's not a single unit I can think of that's not useful and applicable to a common strategy (so good on Blizzard for that). However, because of the racial differences each counter requires unique responses. And, StarCraft II is not entirely a game of counters; sometimes it's a game of just powerful units and powerful builds and combinations.
I don't like thinking of StarCraft II as balanced, primarily because it reminds me of the reasons why I dislike other strategy games; all the units in those other games are pretty much the same. Whereas in StarCraft, you can exploit maps, builds, units, expansions, and even buildings! That is, until the metagame settles down. I think that's what makes TLO such a great player. He knows (or at least tries) potentially powerful builds and just runs with it.
I think a lot of us, the players, are thinking in the wrong context. We see a powerful build or something and we're quick on our feat to ask Blizzard to address it. But we don't realize that StarCraft II is designed on a premise of super-powerful units. I love how Blizzard doesn't immediately address an issue with nerfs, too. They try to find ways around that.
I started thinking this way when I read that Dustin Browder said in an interview that he's just trying to make powerful and really cool units, and that he's not necessarily concerned with balance. At first, that struck me as odd, and since this was pre-beta at the time he said it I was greatly concerned. I mean, he does come from the CnC series (which, imo, is arguably not the same caliber of game that SC2 is). But then after playing the beta, and watching many high-level players and matches, I've come to understand what he meant by that. I really applaud him and his team for that approach.