wat. then why is it available for anyone to dl?
It's not on the main install page: http://store.steampowered.com/about/

People are free to download, but they have a limited beta now. I think they want to make sure they don't have any major issues with a small set of people before millions of people start using it. Just like you can download the Dota2 client, but you have to be invited (or you can buy a pass now) to actually play instead of watch.
 
apparently you can get on steam for linux w/o a beta key by using this
steam://open/friends
im guessing you put it in your browser and it loads it
 
Yeah just used the steam protocol to bypass the beta invite.
Valve games won't work unless you are offically part of the beta invite (no TF2)

A bunch of games seem to be working under steam linux though, check here for more info:
http://www.reddit.com/r/linux_gaming/comments/12qs6z/steam_for_linux_its_here_deb_in_the_link/

How to install steam linux and bypassing the beta
http://www.omgubuntu.co.uk/2012/11/reddit-users-bypass-valve-linux-beta-invitations

I came into a couple of missing x86 packages while installing from the terminal, downloading the .deb file and installing it from the software center on ubuntu is properly easier.