Getting your website to load fast is essential for e-commerce and should be seen as a priorty for any website, be it a blog, forum or social network.
Yahoo! have compiled a very helpful guide for speeding up your website. Firefox users should install the YSlow extension for firebug. This handy tool analyises the speed of your webpage and gives you a grade from A to F based on your page's performance.
A CDN works by using linked servers located at key positions around the world. When a user visits your page the static content is delivered from a nearby location. I.e. if you host your website in the U.S. and most of your traffic comes from the UK then your users will experience a lag time during webpage loading. This is due to the time it takes for your files to be tranferred from the U.S. to the UK. With a CDN your files can be served from a nearby location, thus speeding up your website.
If you are concerned that your website may be slow because of where your server is located then use the URL speed checker from InternetSupervision™. This tool will allow you to monitor the speed of your website from various global locations based on a 30k web page sample.