Is all this worth it? Well, I've managed to get my lists of facts in order, but that's not the world's most astonishing application. There are other things that these lists are useful for, though.
For example, Damian Cugley has a macro package under development for laying out magazines. <#461#>MAG<#461#>TEX's output routine needs to be quite smart, as magazines often have gaps where illustrations or photographs are going to live. In general, each block of text needs to be output in a different fashion from every other block of text. This will be handled by keeping an infinite list of output routines. Each time a box is cut off the scroll to be output, the head of the list is chopped off and is used as the output routine for that box. That way, quite complex page shapes can be built up.
Mainly, though, these macros were written just as a challenge. I learned quite a lot about TEX and needed some TEXniques I'd never seen before. It was also quite pleasing to see that TEX code can be formally verified, albeit in a rather noddy way. Without some sort of abstract view of lists, these TEX macros could not have been written.