OK, I realize I'm a minority voice here but I've had good experience with internal gear hubs and fully enclosed chain cases. In about 1998 or so I got a new steel frame bike with a Shimano Nexus 7 hub. I wore the frame out by late 2004 and gave the wheels to a neighbor. He put that same hub on another bike. Now I've had a Trek Navigator L200 and Nexus 8 gearing since Fall 2004 with no drive problems. 1 broken spoke and 1 rear tire replacement and 1 flat tire before I put the Mr. Tuffy in. The Nexus 8 is a smoother shifter than the 7 and smoother than the SRAM 7 I had before that. The integral generator lighting system has had no problems. When you get a new Nexus hub or mess with the cables the adjustment is very easy, put it in 4th gear and turn the little knob until the marks line up.
I'm one of those people who like the simplicity of these fixed gear bikes but worry about the knees.