latest nightly build of Chromium 11 now has a new two-dimensional logo.
There's absolutely no information about why the change took place -- which is a little bit odd for an open source project -- but we assume it's to further differentiate Chromium from its closed-source and commercial cousin Chrome. The Chromium Code Review page for the patch simply shows Googler Elliot Glaysher approving the change -- and that's it.
An alternative analysis, which is much more exciting, is that the Chrome logo might soon undergo a similar steamrolleresque transformation. We can't imagine why Google would want to re-brand Chrome, however, unless it really is sick of having an 'off balance' logo (it's tilted backwards!)