With Google now even penalizing websites which load slowly, performance becomes an issue for every major website. We have developed and we host websites that have over 150.000 daily visitors and over 600.000 pageviews each day. From the (technical) design phase, through development, to launch, performance is always on our mind.
Performance has many factors, and contrary to what you might think, quite a lot can be influenced. Performance should be a consideration when choosing the hosting environment (servers, server set-up, server-specs, locations), when choosing database, programming language, and the webservice that will run the applications. Performance can also be significantly improved by optimizing database-queries and application code, we can advice on both.
Apart from back-end performance issues, using Content Delivery Networks and optimizing the front-end can drastically improve site performance. Consideration are the way cache and caching proxies are used, as well as minimizing the number of http-requests by compressing and combining javascripts, CSS and by using image-sprites.