On March 14th, IE9 was made available for manual download. Begining, March 28th, Microsoft began to upgrade existing IE9 Beta and RC users through Windows Update.
Now, starting on April 18th, Microsoft will begin to start the rollout of IE9 to Windows 7 and Windows Vista customers.
"We'll offer IE9 to customers via a gradual rollout and expect the rollout to be largely complete by the end of June. Similar to our approach for IE8, we'll use WU to deliver IE9 to users. IE 9 willn't install automatically on machines. Users will have to agree to install IE 9," informs Microsoft.
"For business customers who require time to plan and test their deployments, we'll make IE9 available on Windows Server Update Services in June." WSUS allows use of management tools that make it easy for IT professionals to deploy IE9 in their environments in an automated fashion and at their own pace. And, also note, business customers who don't rely on WSUS have the option to use the IE9 Blocker Toolkit to prevent IE9 rollout via WU until they're ready.
For IE9 in Japan, Microsoft says,
"Our sympathies go out to those affected by the continued earthquakes in Japan. We intentionally delayed the availability of the final Japanese language version of IE9 in an effort to avoid any burden to the local internet infrastructure. The Japanese language version of IE9 will be released on April 25th, and WU will be enabled for Japan at a later date."
[Source: Windows Team blog]