I would agree, a fixed gear isn't for everyone, just as a Honda Insight isn't either.
You only loose about 2lbs by "converting" to fixed, but its more about the efficiency gained through running your chain through fewer parts.
I wouldn't feel too sorry for my knees. There is a vast difference between a good fixed gear and a cheaply built one, and I think that idea mostly comes from heavier cheaper fixed gears, as a lighter bike with light wheels isn't very harsh. I will get flogged if the fixed gear community sees this statement, but I ride with two brakes too, so I don't have to use my knees to brake if I don't want...
I rode for 2 years on a fixed/singlespeed through Seattle, and I could make it up all the hills just fine, and I carried a change of clothes and shoes with me in a backpack. I also have a singlespeed cyclocross bike that would be considered my utility bike if I don't need to go quite as fast
