Looks like Valve is definitely going towards multi-platform support. While the Linux version doesn't do anything as of yet, one commenter got the OS X version r

Looks like Valve is definitely going towards multi-platform support. While the Linux version doesn't do anything as of yet, one commenter got the OS X version running after somebody pointed out that both http://store.steampowered.com/public/client/steam_client_osx http://store.steampowered.com/public/client/steam_client_osx and http://store.steampowered.com/public/client/steam_client_linux http://store.steampowered.com/public/client/steam_client_lin... are valid URLs. Both clients download updates, and the OS X version pops up the new, unreleased Steam application and everything. However, it appears to be in closed beta, since he was kicked off after trying to log in (see http://www.reddit.com/r/linux/comments/butl8/steam_for_linux_testapp_thingy/c0opa13 http://www.reddit.com/r/linux/comments/butl8/steam_for_linux...)