Using a Dell business computer, loaded with a Core 2 Duo E6550 I had a max of 39% CPU usage playing with the new Google logo. Average was about 33% just watching it with Windows XP Task Manager.
This was with Outlook, a point of sale program, and a database program open in the background behind Firefox. Not taxing on this machine. However, for folks with older machines that have not been formatted, de-fragged, virus scanned, etc for years.... this could be crippling.