Page load speed is important for any website. It affects the user-experience as well as Google pagerank when it gets too slow. There are so many variables to account for when trying to improve page load, including page download weight (including all the various assets such as images, javascript and CSS), network latency, browser cache and server headers, server load (requests per second and memory and CPU usage) among others. Yahoo has a very nice guide for client-side performance tips. We're going to suspect the database as the culprit for the purposes of this article, but you should first observe the complete picture before deciding on what to optimize.
Here is a starter guide to optimizing database performance.