I will stick to my own builds, will try the controller but it could go either way on that.
Most excited about what SteamOS might do for the linux graphics drivers and the kernel in general if it is a huge success. I hope they launch with built in EGL support (which they probably won't since neither AMD or NVIDIA support it yet and I doubt they will use mesa since it is so far behind performance wise). If so though they would completely OWN Windows on performance and latency right out of the gate thanks to being able to bypass a display server entirely and render directly to the framebuffer right from the kernel. Plus it is better for developers to have access to the entire system to fix a bug rather than code half asked hacks or wait around for the owner or some proprietary driver to fix it (which most often never happens).
For software and game performance (particularly for competive games where latencies is the BIGGEST issue), this could be a huge win for games, software in general and developers everywhere. But it could also crash and burn. Valve is putting up quite a fight though. Most people don't know/care enough to be able to understand the huge drawback of proprietary operating systems like Windows even for the end user. A lot of enthusiasts probably wouldn't bother spending so much money on custom rigs if they knew that their Windows drivers were using incredibly inefficient workaround pipeline magic hackery (can't think of anything better to call it) that destroys latency and performance and makes developement a pain in the ass. I am not really a linux fanboy as much as I am a hater of inefficiency, and closed software is just that; inefficient, and anything built on top of it will suffer for it, even if we are so used to it we don't notice or care. Some projects might be better as closed source but as an operating system the idea is really rather absurd and NEVER would even exist if not for massive public ignorance.
My hope is that SteamOS will make this glaringly apparent once and for all and I hope Valve recognizes this as the most important aspect of the whole damn campaign (since it really is). After all the public is brutal, and won't accept anything new unless it brings something major to the table. Nothing is more major to a gamer than better performance and latency. Nothing is more major to a dev than to be able to produce better code in less time with easier bug fixes. People will not want Windows if they get 15-20 more fps plus better responsiveness in their favorite game on SteamOS. They could either change to free SteamOS (which will run on most all hardware thanks to the kernel) or buy another $600 graphics card and hope it helps, which one do you think they'll do first?
There are a lot of Windows fanboys out there but as far as the facts go it is inefficient, buggy, unprofessional and unfixable thanks to its closed nature. Linux, or another open system like it IS the future, but I am just hoping we don't have to wait another decade to see it. SteamOS is our best chance for that. A lot of people (who don't understand everything I just said) are already saying "what's the point" but people with such underdeveloped opinions can usually be easily swayed one way or the other so it is up in the air at this point. I for one have already abandoned Windows completely and will probably dual boot Arch Linux and SteamOS for a while until I get a feel for it and decide if I want to make it my main system.