I think SteamOs will be another Android, for the GNU/Linux world: it will demonstrate to non-GNU/Linux users that Free Open Source operating systems are easy to use.
The facts are these: just a couple of years ago the majority of users thought that "linux is too much complex to use". Just because uncle Bill (Gates) told them so. But then Google released Android, and a lot of users tried it: this way they discovered that it is based on Free Open Source Software and it's easy to use. You may like Android or not, but it's undeniable that it has taken away the fear of FOSS from users that have been using only Windows before. Today, every day, a lot of people try GNU/Linux distros for their first time, and they have been encouraged to do this by using an Android system (maybe also by the loss of Microsoft's software quality).
Also RaspberryPi helped, but it's still a too little project, since the majority of users will never use a Raspberry.
Now think about SteamOs: an open source game console system. And it's a real GNU/Linux system, it does not try to hide its FOSS roots (like, instead, Android does). If SteamOs will be appreciated by gamers (and considering the power of Valve I think it will) it could finally show to all World's users that GNU/Linux is easy to use, and more powerful than proprietary solutions.
Will Valve be able to solve Canonical's first bug (https://bugs.launchpad.net/ubuntu/+bug/1)? Maybe not. But it will surely help a lot.
Someone may have noticed that I've not written anything in the last six months. I just have been too much busy with my work. Some people asked me when will I release a new stable version of Kartesio: I hope I'll be able to do the last changes in January.