Cool news, except I don't have a computer with any Mac OS. Plus, I already have L4D1 on my PC, and L4D2 for my 360. Also, I think most people that wanted to play it that bad would've used Wine or whatever it's called, and found a no-Steam version for the games, if there is one.
You should quote info from the source just for convenience. Any who, here's the info...
Left 4 Dead 1 and 2 are coming to the Mac!
We like the platform wars in the forums so much that we've decided to add a new platform to the fray. Later this spring, we'll be releasing both Left 4 Dead 1 and 2 on the OSX operating system for Mac computers, all through Steam.
Steam on the Mac will behave just like Steam for Windows, but through Steam Play will add cross-platform ownership. That means if you own Left 4 Dead 2 for Windows, then you already own it for the Mac. There's no need to buy it twice! Unless you want to buy it twice, in which case, as long as you're feeling so generous, why not buy it five times?
Plus, Mac and Windows players can go head-to-head, since both Left 4 Deads are cross-platform compatible. Mac owners can even host their own servers and create their own maps, just like Windows users.
The Mac Versions of L4D1 and 2 don't run under emulation software but in native code. That's technical talk for how cool your friends will think you are with your five copies of Left 4 Dead 2 for the Mac.
We'll be releasing the exact system requirements soon. The Mac versions will be updated in sync with the Windows versions, so the platform wars can continue uninterrupted.
Even though Left 4 Dead 2 is the only game you'll ever need on any platform, as a purely academic exercise, you should probably check out the complete catalog of games available on the Mac when the Steam client is released in a few weeks.