I know many, many people that would never even consider switching to Linux until Office and the Adobe suite are first-class citizens.
As happy as I am to see Steam come to Linux, I don't expect Linux to grow much desktop market share as a result. The future of user-facing Linux is Android.
A common complaint against Linux game development is that it lacks a standarized platform and different distributions have their quirks. While I don't like Steam and don't use it (DRM, no resale, obnoxious pop-ups...) this is going to give game devs/publishers something to target. In my opinion it will be more psychological than practical. Source engine games, one or unrelated two AAA show up - and suddenly minor devs are starting to think "Why not ? Me too !".
I don't delude myself, though: several dozen percent games still won't show up on Linux. But it beats having to rely on the 5% games that are multiplatform.
As happy as I am to see Steam come to Linux, I don't expect Linux to grow much desktop market share as a result. The future of user-facing Linux is Android.