You might have heard about Google Chrome OS right? It was announced in 2009 and in this year's Google I/O conference, Sundar has officially announced that Google ChromeOS (which will be called ChromeBook) will be available by this year and they have a joint cooperation with several vendors to provide you a netbook with Google ChromeBook pre-installed.
If you just curious about ChromeOS, but you don't have a feel of buying the netbook, then you can try the ChromiumOS Vanilla Nightly Build by Hexxeh. They provide you with daily build of ChromiumOS, available for VMWare, VirtualBox, and USB Flash Drive image, so you can install it on your desktop/laptop or you can bring it everywhere on your portable flash drive. It's around 214 MB, so 1 GB of flash drive would be sufficient for the image.
Follow his Twitter account for future updates.