I feel that once you begin reaching full capacity of any sort of web server or begin seeing the bottom line dramatically affected by the number of users on your website, it’s time to begin looking at efficiency in serving up data to your users. A couple of the best experts, who you wouldn’t quite think about, are Yahoo and AOL. These are two companies who make their profits in providing data via the web, content. And as these companies have been around for so long (relatively) and been through their ups and downs, they have found themselves in the unique position of performance and efficiency.
Yahoo specifically, has released a set of performance best practices, many of which I completely agree with. Some include using CSS sprites, minimizing HTTP request, and minification of JS and CSS. There are a lot of other really good pieces of advice as well. If you are a web designer / developer, you should definitely take a look at these.