More than 1.5 million copies of Valve's acclaimed action puzzler Portal have been downloaded since the developer started offering the game as a free download to celebrate the launch of Steam's Mac client, the company said today. Valve didn't provide a breakdown of how many downloads were of the PC version versus the Mac version. The game is one of a growing number of titles offered through the Steam distribution service that use the new "Steam Play" feature, giving players access to both the PC and Mac versions of compatible games with a single license. Portal became free last week, and that promotion will continue through May 24, after which it will again be sold as normal. Along with the 1.5 million figure, Valve provided a couple of rough statistics about its Mac users so far: Two thirds of them are running on laptops, and 11 percent of Steam purchases in the first week of the Mac client's availability have been for Mac. Valve says it will soon expand its widely-reported Steam Hardware Survey, which compiles extensive data about the computers Steam players use to run their games, to Mac hardware as well. Finally, the company offered one last stat sure to set plenty of game forums ablaze: Portal is one fifth as likely to crash when running on a Mac than it is when running on Windows.