Adam Barth, a software engineer at Google, on the Chromium Blog:
This was not an easy decision. We know that the introduction of a new rendering engine can have significant implications for the web. Nevertheless, we believe that having multiple rendering engines—similar to having multiple browsers—will spur innovation and over time improve the health of the entire open web ecosystem.
UPDATE: As Guy English reminds us, The Doctor has already chimed in on Google’s new rendering engine.