Let’s erase one claim right off the bat. The headline, “Using ‘Free’ to Turn a Profit”, is misleading and downright false as it relates to the subject of the story. Near the end of the piece Phil Libin, the chief executive of Evernote, says they are generating about $79,000/month in revenue. Then the article goes on to say “By January 2011, Mr. Libin projects, the company will break even.”
Everything is cached so it only does the minification and hash calculations once per file. We’re obviously running FastCGI so the in memory cache goes across http requests. More importantly the js/ dir is statically served by the web server so it’s exactly as fast as it was before we did this (since we served the .js files without any preprocessing). All this technique adds is a couple filesystem stats per page load, which isn’t much.