http://github.com/cloudhead/less.js/blob/master/benchmark/be...
Which has all the features of LESS in it, and weighs 94KB (3600loc), compiles in 130ms on my macbook pro.
I would say that's plenty fast. You can try it out by running `$ make benchmark`
It's also worth mentioning that plenty of people who care about page load times would still care about 130ms. It's not as glaringly awful as 1.5s, but it's definitely comparable to the sorts of times under discussion. See http://developer.yahoo.com/performance/rules.html and http://code.google.com/speed/page-speed/docs/rules_intro.htm...