De acordo com o site
Performance Note: Google Chrome Portable may run slowly from some flash drives. You can speed this up by copying GoogleChromePortable.ini from the GoogleChromePortable\Other\Source directory to the GoogleChromePortable directory and editing it to set RunLocally=true. If you do so, be sure to allow Google Chrome Portable time to copy your profile back after shutting it down. Of course, there are privacy implications to copying your personal data locally to a PC not under your control.