The current version Google Toobar 8 was a part of Google Toolbar Labs project. Google Toolbar Labs is the place to test the newest ideas and technologies for Google Toolbar. Labs toolbars may not be as full-featured or as stable as Google Toolbar, but they will be a cutting-edge way to try out new features, provide feedback, and help improve our product. Google Toolbar 8 for IE9 is actually built and runs on top of the Google Chrome Frame platform. This means that Toolbar 8 will run more like a web app in that it can be customized and updated much more frequently and easily. It also means that Google Chrome Frame is installed at the time of Toolbar 8 installation, and all the benefits of having Google Chrome Frame come along with it.

Since this is a brand new platform, not all Google Toolbar features are available. There are, however, a number of new features in Toolbar 8:
Google Instant
Google Dictionary
Most Visited Sites

The new toolbar can auto-update even while you are browsing, so you will get the latest version instantly without having to restart. If you are using Google Toolbar 8, you will be updated frequently so that we can fix bugs and add new features more quickly than on previous toolbars.
But testing is closed right now and if you try to download it you still get v6 I think.

Toolbar 8 FAQ : Toolbar 8 (Labs) - Toolbar Help

Google Toolbar Labs