A colleague just pointed this out to me - very cool. I’d rolled my own solution along similar lines, but it’s not as comprehensive - so now I’ll need to figure out a way to transition my existing style sheets.
FWIW there’s a .NET port of .LESS here: http://www.dotlesscss.com/
People have been clamoring for CSS variables for years, but there are what seem to me to be good theoretical reasons not to do this; see http://www.w3.org/People/Bos/CSS-variables
I think that server-side or author-side solutions along the lines of .LESS are going to be the best solution to this problem for the foreseeable future.