I would be very interested to see a single real-world use for a fixed-point combinator. I have a reasonable understanding of what one does, but I still haven't got the faintest idea why you would ever need one, nor have I seen a single situation in which applying one doesn't make the situation unimaginably more complicated to understand.
As an alternative to the zipWith method of calculating the Fibonacci series, you can use scanl, resulting in (in my opinion) an even more elegant version:<p><pre><code> fibs = fix $ (1 :) . scanl (+) 1</code></pre>