This is a bloated comment on: http://blog.sanctum.geek.nz/advanced-vim-macros/
Sharks in Shells
Firstly, there are at least two plugins that can tabulate text in vim: Align and Tabular. Using plugins written in pure vimscript is usually better than shelling out to system tools, because it's more OS independent. On that same note, Vim has a builtin :sort command, so no need to shell out for that either.
You warn against reaching for the hammer when holding screws; that it's sometimes better to use a splash of :ex and a sprinkle of VimL. Indeed, that is true in this example (starting with the cursor on the first line of the original data table):
:Tabularize / \+/
Mentioning Macro Mechanics
Yanking a macro line from your buffer into a register with "ayy captures the trailing ^J which, if you have something bound to <Enter>, will produce unwanted side-effects. Use ^"ay$ instead (or the VimLocalMacros plugin).
When assigning macros in a let expression, the double-quote form does allow for Vim map-style markup:
let @a = 'must have ^M literal chars'
let @a = "can have \<cr> escaped markup"
There's no inherent benefit from moving this sort of macro into a function - it's so uniquely dependent on your current text file (and year!) that it simply doesn't make sense in this case. However, this trick might be useful in more generic situations. Using a function to preserve macro contents allows us to reuse the register that macro was occupying. Personally, I use macros on an ad hoc basis, crafting them quickly for the need at hand and discarding them when done. I might overwrite register @a several times over within a single edit session with various macros on an as needed basis. However, I was asked one day how to persist particular macros for a given file. The embedded-in-a-function approach shown in the article is one solution. I also wrote VimLocalMacros for this purpose.
Macros stop executing if an error occurs. You can use this to your benefit. Design your macros so they deliberately fail - easy way to not have to count and just provide a large-enough number of runs: 999@a
Recursive Macros have a use and are not something to be dismissed as the wrong tool instead of reaching for a scripting language.