I think what Linux gaming and the Steam Linux client really needs above all else to even begin to make anything like the difference people are hoping for, is (good) games which are exclusive to Linux... and it's a big ask - what developer would willingly restrict their game from the biggest sales channels? (not even Valve... I'm not sure)
It's certainly a start to have some of the existing titles running natively on Linux, but for example I've installed TF2 to see what it was like, and it's alright, if I've booted into Linux to do some non-gaming related stuff and suddenly fancy a blast of TF2 maybe I'll use it, but there isn't a good reason for me to do so other than this slight convenience.
Imagine if Valve took Half Life 3 or a similar highly anticipated release, and made it Linux exclusive for the first year or 6-months... The problem with their current promotions like the exclusive "penguin" item giveaway for TF2 is it doesn't achieve its intended goal of encouraging people to give linux a try. Instead it just encourages a bunch of TF2 kids to have a bad experience trying to aquire said item and vow to stay away from Linux forever. The amount of time someone wanting to play HL3 without the wait would have to spend actually using the OS to complete the game, some are bound to discover that they actually kinda like it (and those that don't get on with it can just pick it up when it makes it to the other channels). On the other hand maybe 99% of people would just wait until it is released elsewhere.
