Google's code is immaculate, their products are ubiquitous. Which is not to say that they haven't made a few missteps, but whether you like them or not, they've made your internet experience better. It's called the Wal-Mart effect: a few stingy shoppers harangue Wal-Mart to keep their prices low, but you get the benefit of their labors just by shopping there. In this case, Google reinvented e-mail with gmail, and it was so successful that Yahoo! and Hotmail copied them--hence, you get more storage on your Hotmail account. Or there's Chrome, Google's web-browser, which beat the pants off of IE and Firefox in speed tests. Microsoft and Mozilla stepped up their game in response, and you get the benefit of a faster browsing experience no matter which browser you use!
Also, they do something with search engines, I forget what exactly.
Now take a look at Valve. Yes, I've been wigging out over Portal 2 news and gushing over Half-Life, and I'd hoped to leave it at that. And then yesterday Valve announced that their distribution client, their gaming engine, and their entire catalog would be coming to Mac this spring.*
With all the platform wars going on, Valve decided the best way to do things was to open the field to more players. You know the Soul Caliber series of tournament fighters? In the last two numbered installments, the game had a difference "bonus" character for each platform. In Soul Caliber IV, for instance, XBOX 360 owners could play as Yoda, while PS3 owners could play as Darth Vader. If you want to play as both... well, you have to buy two versions of the game. It was new, it was innovative, it was downright dickish.
If you read the press-release from Valve (same link as above) regarding Steam-for-Mac, they say over and over that from now on, all their releases will be simultaneous for Mac, Windows, and XBOX 360. Games will run on native code, not emulation. They will be simultaneous builds, not ports. Furthermore, if you own a copy of game for Windows, you automatically get a license for Mac at no additional charge. In short, they've decided to take "gaming" away from Microsoft, and they've made pretty clear that the Mac version will not be some ugly younger sister, but will get the same treatment.
This is pretty groundbreaking, and it's one of the reasons I've come to respect Valve so much. What does this mean for you? Well, probably nothing, unless you count the Wal-Mart effect. Since Valve is catering to Apple and has re-written their distribution client to be compatible, they're going to be encouraging other game developers to write for Mac. Which means other software developers will begin to follow suit. So, if you're a Mac-user, you'll have more software available and if you're a Windows user you'll be better able to interact with Mac users.
And the world slowly becomes a more open place.
*to clarify: the Steam client distributes games that are not made by Valve, and obviously not all of those will be Mac-compatible, but everything Valve makes will be.