The fastest browser for windows has been getting some major updates at it gets ported to Linux (& Mac). Chromium is not officially a Google Chrome browser, but developed under the wings and support from Google. Chrome is built from Chromium, the distinction is intentionally made perhaps to separate the Google Chrome brand.
As it is the case with any alpha releases, there are many bugs and unsolved issues with this version.
Chromium developers goes as far as encouraging you to not use this version on the default loading page. I personally saw problems with default fonts and flash (doesnt work). But as far as page rendering is concerned, even in its alpha stage Chrome for Linux is the fastest Linux browser available yet.
You can download debian / Ubuntu alpha builds from here, and if you are brave (and using other distros) install it fromt the source.