And here are the results. The best browser for each test is highlighted in green, and the worst is highlighted in red.
Startup 10 Sites 25 Sites 25 Sites After 10 Minutes Close Tabs
Firefox 3.5 29.5MB 63.2MB 136.0MB 135.8MB 69.3MB
Google Chrome 2.0 29.2MB 152.8MB 279.9MB 172.4MB 56.9MB
Google Chrome 3.0 Beta 39.5MB 260.9MB 389.4MB 197.6MB 53.7MB
Internet Explorer 8 37.0MB 184.3MB 400.8MB 402.4MB 67.6MB
Opera 9.64 21.3MB 62.2MB 166.4MB 151.6MB 135.9MB
Opera 10 Beta 25.5MB 70.4MB 175.0MB 179.0MB 186.2MB
Safari 4 28.5MB 109.5MB 231.2MB 241.8MB 198.4MB