If you find yourself, as I do, at the coalface of sysadmin _and_ accounting (or sysadmin and engineering, as the author does), I wholeheartedly recommend the Numderline [sic] patched fonts for making it much easier to see the size of large numbers.
Numderline uses OpenType features to automatically group thousands in any sequence of numerals longer than three.
You can patch your own favourite font with one of several grouping techniques, but I'm happy with the sample fonts that the author has already done.
