While Starcraft 2's balance is currently in a fairly nice place, there is a bit of a problem with certain tactics and units being far superior than their counterparts which tends makes matches predictable, and consequently boring for the average player. In an effort to fix this, and also make Starcraft 2 much more exciting to play, Blizzard has just announced a variety of massive balance changes and unit reworks.
The amount of minerals present in each base has been slightly increased in order to give players the ability to mount a comeback, numerous units and abilities have been completely redesigned, the obnoxious Widow Mines have been made easier to clean up when unattended, the Protoss Mothership Core has been entirely removed, and the list goes on for quite a while. There are simply far too many changes for me to summarize, so if you're interested in all of the details you should head over to the Starcraft 2 website.
I'm not exactly sure how all of this will affect the balance, and to be perfectly honest I don't think Blizzard does either, but this is definitely a step in the right direction. If Starcraft 2 is to survive it needs to maintain both a casual and hardcore playerbase, and what better way to do that then by making pretty much all of the fun units competitively viable while also nerfing the annoying ones. The specific date has not been announced just yet, but you can expect to see this update at some point in November. Personally, I can't wait!