For Dry Fly Fishing 9' leaders are very common. If you go much longer accuracy suffers, go any shorter and the presentation and length of dead drift suffer.  

There are three common styles: knotted, knotless and braided. Knotted leaders are mostly hand tied using ever smaller diameters of leader material to get to the desired tippet size. Knotless leaders are extruded and the sections are formed and ends are sized during the process. Braided leaders are two piece. The butt and midsection are braided from a fine monofilament and each end is generally looped.  The butt section loop is connected to your fly line and the other to your tippet.