I remember the first time I went to the Salmon River and I saw these guys with like 13 foot rods, and giant fly reels totally spooled with mono. I first thought they were crazy but after watching them, I found it to be pretty damn intriguing.
Turns out they were pinning. You suspend a fly, bead, or lure under a float, and these centerpin reels would peel off line as current pulled the float downstream. This allowed you to get a drag free drift pretty much as far as you could see downstream. With typical chuck n' duck steelheading on a fly rod, you might get a proper presentation for about 10 feet. With pinning, you get a fly properly presented for about half a football field.
I have a co-worker that frequents the SR and pins whenever he can, and he's shown me some pics of some monster fish he's landed using this method. Turns out that he actually makes and sells centerpin rods and has an instructional video for using them. You can check them out at Troutpin.com.
Here's the video, which gives you a great overview in case you've never seen this method before.