The builds for Mac OS X come straight from the Chromium project, the open source effort underlying Google's Chrome web browser. Chromium for Mac is still very rough around the edges, but new builds appear faster than you can blink. Sadly, they appear to be Intel-only; I tried them on my PowerPC Mac, but that's a no-go for now. I certainly hope any eventual Google Chrome for Mac releases are available for PowerPC as well.
Moving on to the Windows variant, one of the most requested features for Chrome is a plugin framework, to allow for the same extensibility that for instance Firefox can offer its users. Chrome 18.104.22.168, released in the dev channel, includes the plumbing for such an extension framework (detailed changelog).
The team working on the extension framework detailed their progress in a post on Google Groups. "The extensions posse would like to point out that as of today's dev channel release (22.214.171.124), extensions are starting to be a bit more useful. We can now put little bits of UI in the chrome of Chrome, and some of the APIs are starting to come together."
There's a how-to page available for building Chrome extensions, as well as a page with a few sample extensions.
All in all, it appears Chrome is growing up. The Mac version is coming together, as well as the plugin framework. I continue my idle hope that there will be builds without this framework built-in, but I guess that will be in vain.