This page is useful for comparing the user experience of two pages. Note that the two pages could interact, thus altering the true results. You can load the pages individually ("Load 1", "Load 2") and compare them based on load time. The "load time" is measured by instrumenting the onload event of each iframe.
Google vs Yahoo!: Search | Calendar | Finance | iGoogle vs. My Yahoo! | Maps | News | Picasa vs. Flickr | Groups