Adobe is shipping CS4 today, as well as Flash Player 10. Adobe TV has new training, with new movies for AE by Chad Perkins and Mark Christiansen. Adobe Support has also been updated and renamed as After Effects Help and Support.
Other training is now available at Lynda.com, Total Training, and elsewhere. Additional resources on CS4 were listed in previous posts.
Update: Motionworks posted a new movie, New Features in After Effects CS4: Part 1. And later New Features in After Effects CS4: Part 2.
Update 2: Chris & Trish Meyer have some reminders and links on the upgrade in After Effects CS4 is Shipping.