Shared hosting migrations started around 2 months ago now and have been making steady progress - it's a lot of work migrating thousands of websites! We're over halfway there and aim to be complete within the next 4 weeks.
Many of you will already have been moved and know the in's and outs. The rest of you will receive your migration email in the next few weeks which will specify your date and time of migration, together with your new server details. You can refer to this earlier blog post for more details about the migration.