I truly do hope that Valve comes aboard the Linux platform, because then the door will be open for other gaming companies to do the same. The Linux platform desperately needs a solid gaming scene to attract more "Windoze" users to make the switch.
One more thing, checkout this web site:
I encourage all Linux users to check this out and to send in e-mails to encourage support for the Linux platform. It sounds amazing and so far they seem to be only supporting Windows and Mac OS X. From what I've read they use a browser plugin to transfer the latest 3D games to PC's.