After steam self update, I reopened it and a popup informed that the steam client is out of date and I have to update it via downloading the latest .deb, or the repository. So I tried to find the official repository of steam, I found this URL: http://repo.steampowered.com/steam/,
but no easy-to-copy-and-paste console commands as usual.
So I've managed to add the repository with this commands:
For the repo key:
&& sudo apt-key add signature.gpg
And the repo line for sources.list:
(If you add this line via Software Sources or add-apt-repository you must comment/unmark the deb-src line or the apt-get update will fail)
I've tested this on an ubuntu 12.10 x64, I hope this helps.