When we announced the migration tool last month, we pointed to the week of February 22 for its launch. That week is upon us, and we're just about ready to launch. We're doing some final QA on the tool, and will get it launched this week. Exact launch date is subject to a few variables - but we will update the blog as soon as it's available.
Once launched, you'll see an alert in your dashboard if you have any FTP blogs to migrate, and will be able to get started right away.