Extension support is active again and bookmark synchronization has arrived in the Google Chrome developer's build for Mac OS X. Default extension support was disabled in Chrome for Mac in December, followed by promises that it would be re-enabled within a month.
Bookmark sync does not yet work flawlessly: a known bug related to the sync process will crash the browser when you add a new bookmark folder.
The latest developer's build, version 4.0.288.1, is available for Windows, Mac, and Linux. Windows users will only see two bug fixes: one prevented HTML5 audio and video content from not loading, the other stops content scripts from running twice on some occasions.
The Mac and Linux versions, being further behind in development than the Windows version, offer more new features. In addition to extension and bookmark sync support, and fixing the aforementioned HTML5 and script bugs, Google added for Macs "pin tab" as a context menu item, included a "learn more" link on the crash page, and baked in the Esc key as a shortcut to stop the page from loading.
Mac users should also note that to switch from the beta version to the developer's build, you'll need to manually download and install the developer's build. The automatic upgrade path from within the Chrome beta won't work because it's a different development channel--even though they did share version numbers.
In brief testing, both the bookmark sync and the extension support work without problems. If you encounter any problems in the latest Chrome dev, tell us in the comments below.