There are few things that are more annoying than a slow web site. However, what constitutes slow? Rule of thumb is if a site takes more than about two seconds to load, it is considered slow. Problem #6:

A slow Drupal site

Occurs when
Your site takes more than about two seconds to load.

Fix by
It can be fixed by turning on caching, upgrading your server or changing your hosting company. There are also more advanced caching mechanisms you can use. For more info, refer to Chapter 7, RSS Feeds, Site Speed, and SEO Testing in my book, Drupal 6 Search Engine Optimization.