Knuth points out a very useful property of the Fibonacci number base: conversions between kilometers and miles.

All you do is shift the digits!
For example, say I want to convert 65kmh to mph. Well, 6510 = 55 + 8 + 2 = 100010010fib, and shifting (right) we have 10001001fibmph = (34 + 5 + 1)mph = 4010mph (it's actually closer to 4110mph).

Details of why this works are left as an exercise to the interested reader.