Preview of iPhone OS4

Sneak peek from Apple

Also see:

New iPhone system, with multi-tasking, unveiled — from CNN.com

and

iPhone OS 4: Multitasking and 100 other new features — from wired.co.uk

and
Apple Previews iPhone OS4: Mutli-Tasking, Folders, Gaming Platfrom, iAds
— from gottabemobile.com