Also, Team Fortress 2 for Linux  was officially released today (it's been in open beta testing for quite a while).
What I find particularly interesting about this is the time-limited item giveaway. Valve did something very similar when they released the OS X version of TF2, where anyone who logged in on a Mac received a free cosmetic "earbuds" item. The promo triggered a mad scramble of players to find a Mac to play on, and when it ended, the buds acquired a huge scarcity value -- they currently trade at the equivalent of about US$30 a pair, even though they have no effect on gameplay.
I don't think the penguin will end up valued as highly, but what it will cause is a sudden influx of relatively non-technical gamers trying out Ubuntu for the first time. Should be interesting to see what pain points and rough edges they expose. There are already tech support threads popping up in the Steam forums, e.g. 
I'm quite amused by Valve's business decision. One may say that this is the logical next step but I'm smiling on the insides. I can't help but think that they're tryig to out-Microsoft MS. The embrace, extend, extinguish policy is obvious as day.
They waited all these years to gain a significant foothold in the Windows segment. Now that they've got this, we could see them slowly expanding to Mac first, and today Linux. I mean, it's certainly a huge incentive if you're given ready access to your game library on the other OS, even though you didn't expect it when you purchased the game on Windows months or even years ago. Screams of extend. I just wait to see if the market forces themselves will play the 'extinguish' card or will Valve play it?
Once Office and a decent number of games port over to the penguin, I'm really confident that the only people who use Windows will be (a) people who know nothing about computers and use whatever it came preinstalled with (b) at work since they're not allowed to format the computer (c) they need a very specific software that is not available on Linux or Mac (Ansys etc.)
The tipping point will when/if a major OEM starts offering a large quantity of their products with a Linux distro as the default OS (i,e you have to specifically select Windows).
Realistically Steambox would seem to be the most obvious place for this to start happening. Of course how much the Steambox will be a "real" Linux computer vs just a kernel+whatever the minimal software stack is required to get Steam running remains to be seen.
I wouldn't hold out much hope for an Office for Linux regardless of what Phoronix thinks. Porting office to Linux would be a tantamount to MS admitting they have given up on Windows and would probably hurt their stock price significantly.
From a technical point of view the biggest thing that would make Linux a viable choice for the majority of desktops would be a WINE layer that provides at least as good compatibility as Windows XP for Windows software thus allowing legacy VB6 etc stuff to be moved over.
> I'm really confident that the only people who use Windows will be (a) people who know nothing about computers and use whatever it came preinstalled with (b) at work since they're not allowed to format the computer (c) they need a very specific software that is not available on Linux or Mac
Or OpenGL graphics programmers who find the state of drivers under Linux, while a lot better than years ago, still sub-optimal compared to Windows...