I bought a couple of the Dr. Slicks from Sierra Tradding Post when they had them on closeout. I often ask the question to other fly fisherman: "What if I could increase your landed fish percentage by 20% for under $15 would you buy a fly fishing accessories?" They look at you like "OF COURSE I WOULD". Then when you tell them that the accessories is a file they just don't believe it. I made up the 20% of course but how many times have all of us had that 5 or 6 bites in a row that did not end up in hook up, much less landed fish? I won't fish without a file in my vest. Most of the time I tie on chemically sharpened hooks like TMC or Mustad Signatures these days but it is not the out of the hook or fresh out of the box sharpness that bothers me. I need something to touch up the hook while fishing rocky structures or bluntly after landing a few fish. Just a couple of strokes makes a huge difference.
http://www.orvis.com/intro.aspx?dir_id=758&subject=2108
http://www.chron.com/disp/story.mpl/sports/3670113.html