This is huge news for Mac users who enjoy playing Source-engine games (Half-Life 2, Team Fortress 2, et al). Apparently in preparation for these titles to debut on Linux, Valve has done some optimization that has provided a major benefits to OS X users. As of right now, the beta is only available on certain titles, including Half-Life 2 and its expansions, Portal, Team Fortess 2, Counter-Strike, and Left4Dead 2. I've probably left out a couple others, but you can see what's available by right-clicking on the game in your Steam library and entering properties and looking for the "betas" tab. To actually obtain the updated game, you need to delete any games you want to beta test but already have installed. Once you've deleted that content, go into game's properties/betas tab, opt-in from from the drop-down menu, wait for the confirmation to appear in that box, close it, then re-download the game. Half-Life 2 and Portal are about 3.6 GB each. While I've not run any official benchmarks, the performance difference is night and day. Previously, in order to maintain a steady framerate on the MBP in my signature, I would have to turn down the resolution to 1440x900 and lower the details. Even then I would see occasional slowdowns. With the SteamPipe editions, HL2 and Portal are pretty much locked at a solid 60 fps at 1680x1050, high details, and with anti-aliasing and anisotropic filtering enabled. During a brief session of HL2, I only saw one slowdown and that was with something exploding right in my face. As far as I'm concerned, the performance gap between OS X and Windows in these games is essentially closed. Unfortunately, Portal 2 is not part of the current beta set. Hopefully it will be in the very near future as I have to imagine Valve will want it ported to Linux, too.