I believe that it uses the Linux kernel and that makes it Linux since that
is all that Linux is, a kernel. Chrome OS is an operating system just in the
same way that Ubuntu is and both use the Linux kernel. I believe that Ubuntu
actually assisted Google in the endeavour. What makes ChromeOS different is
that it will be stripped down and have its own window manager that can only
access the web.

See:
googleblog.blogspot.com/.../...ogle-chrome-os.html

You can get a working version of Chrome OS Flow here:
maketecheasier.com/.../29

Just download and follow the instructions.