Chromium OS boots extremely quickly and makes Google Chrome your operating system instead of, for example, Windows. Since this is done from a USB drive, just remove the drive and restart your PC if you want back into Windows like normal. A 2GB or larger USB drive is required.
Download and extract Win32diskimager. This works without being installed and is used to write Chromium to your USB drive:
win32diskimager-RELEASE-0.3-r27-binary.zip
Download Chromium OS from this page, use the first USB image download link (it includes drivers and a built in updater):
http://chromeos.hexxeh.net/
You will need to have a program installed like 7zip or winrar; extract the gz file to tar, and the tar file to img.
http://www.7-zip.org/
Then run win32 diskimager and write the Chromium image to your USB. This will erase all data on the USB. Now boot your computer (or any) from the USB to use Chromium!
The first time you login you have to use the following credentials
username: facepunch (@gmail.com will appear automatically, this is fine)
password: facepunch
Once you get connected to the internet, restart and use your regular Google login.
Right now my laptop will not open addresses that start out with https:// in Chromium for some reason, sounds like most people don't have any problems.