Hey - I have pondered using less / sass / etc but so far haven't yet had much need (though the repetition required by the theming is perhaps a strong case to start considering it). To be honest, the vast majority of the site's CSS is contained in Twitter's bootstrap framework anyway so up until this point it's not something I'd worried much about :)

If you're using bootstrap, it's even better to use less; it includes a load of mixins for things like border-radius etc.

Just @include "bootstrap.less" at the top of your less file, add your rules below and compile just your less file using lessc. Easy.