Learn iOS4 in 10 min: video quick-start guide
If you just want to know about all new iOS4 features quickly here's a great video that introduces iOS4 in 10 minutes. iPhone 3GS is used in this video. If you have iPhone 3G or iPod Touch 2G you won’t get the multitasking.
Let's watch:
via tipb
UPDATE: Learn iPhone 4 in 10 min: video quick-start guide