The feature is not enabled by default and we hear it's still a little buggy, but that's something to expect when running the dev build. To enable extension sync, right click on Chrome's shortcut, choose Properties, and at the end of the Target field add the following command line switch: "--enable-sync-extensions" (minus the quotes).
The other big new feature in Chrome's latest dev release is the built-in PDF viewer. In its current implementation the feature is fairly limited and appears to be based on the same technology that powers 'View as HTML' in Gmail. This means users are not required to have Adobe Reader installed, which could provide safer experience for those who often drag their feet when it comes to installing new versions of the plug-in. Google will still allow Acrobat Reader -- or any other PDF reader -- to be launched directly from Chrome in case you need more advanced capabilities.
If you are interested in trying out the new features just head over to the download page for Google Chrome's dev channel builds. If you don't want potentially unstable software running on your machine, though, it might be better to wait for these features to trickle down to the beta and then the stable release channels.