The move doesn't mean a radical new version of Google's browser is available to test--the changes over the 5.0 series are pretty minor, chiefly reflecting the fact that a new branch has sprouted from Chrome's source-code tree. But the change is important for a couple reasons.
First and foremost, it means the work of buttoning downand other can begin in earnest since experimental work is now happening elsewhere. Chrome 5 will be the first stable release for Mac OS X and Linux, a move that's important for attracting mainstream users.
Second, starting Chrome 6 frees the cutting-edge coders up for developing those new features, making the new branch more than a mere twig.
Google doesn't make a big deal about Chrome version numbers, treating them as mere milestones passed on the journey to a better browser. If a feature doesn't make a particular milestone, it gets pushed back, as indeed has happened with a few items planned for Chrome 5. But Google updates Chrome relatively frequently, so delaying a feature typically pushes it back only a few months.
Chrome updates are installed transparently in the background by default, a move that might cause some indigestion among those who want to stay in charge but that ensures that nobody is.
So what exactly are the new features in Chrome 6 so far? Nothing major, according to a blog post from Google Chrome team member Karen Grunberg. Most significant are some further to better handle right-to-left languages and copying Web addresses.