Opera has been my primary browser since version 9 or so. When I heard the announcement that they will use the Chromium engine I was actually quite happy. They have been contributing to web standards a lot and with the power of the Chrome community I'm sure we will see big innovations.
However this preview release is a big downer for me. I know it is a work in progress but it is missing some key features like the RSS reader, the ctrl + z combo to bring back closed tabs and many more. So I'm not switching just yet but I'm hopeful.