For years I've had an Xbox 360 wireless controller adapter attached to my PC. I have the cable rolled up short and tied with zip ties and have velco on the adapter and my PC so it fits snug in the back on the little corner just for it. It has been my default controller since I first built my Crysis PC back upon release.
To control windows and my OS outside of games, I have used one of these:
It's a gyration MCE remote. It works as a keyboard that you can reprogram in Event Ghost, and if you press the button in the middle of the remote, you can use an IMU inside to control your mouse like a wiimote. This little remote is what really lets me fully use my PC on my Television from across the room. Having a mouse that you don't need a desk to use is incredibly liberating.
All that said, I am now going to completely replace my Xbox 360 dongle with the Steam Controller dongle, I see no need to really ever use an Xbox controller on my PC again. On the off chance that I absolutely need an xbox controller, I can just plug it back in, but the Steam controller is good enough to satisfy basically every game I would ever want to play (and for specialty games, I have racing wheels, and flight sticks, and fighting sticks, although the steam controller is adequate at those as well). And, while I will keep my gyroscope MCE remote (because it is also a universal remote that controls my stereo), I don't find myself having to put down the control and grab the MCE remote frequently. In these last 3 days, I've gone very long stretches using my PC exclusively with the steam controller, switching from playing games to browsing the internet to using Kodi/XBMC.
The steam controller is a great gaming controller, but I think the real benefit of it is the way it makes your entire PC playable from your couch - internet and all. I think it'll see great success with the HTPC market. Hell, even if you don't have an HTPC, you can use it on your phone and output your phone to your TV and still use XBMC/Kodi and browse the internet with the thing. It works on android, and would probably work on iOS too (I don't have any iOS devices to test it with).
EDIT:
That said, I am a tinkerer. I like spending time setting all my stuff up exactly like I'd like it. I'm the sort of person who creates steam grid banners so all my games in steam have icons. I add non-steam games to my steam client to unify ubisoft and ea games within steam. I am looking forward to going through each game in my collection over the next several months and, one by one, creating very customized controller schemes just to my liking, which will take hours and hours and hours.
I've always enjoyed doing stuff like that. For people who don't like tweaking everything to their liking, there is a profile system, but I'm not sure how quickly it'll be populated. I've been going through and setting up "Xbox-like" configurations for all my games that are essentially the Xbox 360 controls mapped to the steam controller, but with mouse look and small fixes to make it work better. And I've been publishing those as well. But looking at my library, I haven't seen too many other profiles yet. Hopefully, when everybody joins in, there will be more profiles.
I'd also like it if Valve could extend the curation system to controllers. If you find someone who plays games in generally the same layout as you do, it'd be cool to follow them and have them automatically set up your gamepads for you.
one preface about my love for steam controllers:
I've used trackball mice for decades.
