Speed really matters, especially on the Web. Is your page loading fast? Woot, you added some cool fancy widgets? Do you know how slower your page is loading now? Can you imagine how much users you've lost because of that? Amazon lost 1% in sales because of loading page time increased just on 100ms, Yahoo experienced 5 - 9 % drop in full page traffic because of +400ms in page loading times, people googled 20% fewer because of Goog's 500ms page loading time increase. Speed matters! Be sure and watch this presentation for more info:
Outcome: if your site is slow, users will visit it less.
Here is a cool tool to measure your page loading times: http://tools.pingdom.com