features of iOS4

What’s new:
-Homescreen wallpapers
-Folder organization of the homescreen icons
-Multitasking and fast app switching
-Google/Wikipedia search in Spotlight
-Bluetooth keyboard pairing support
-SMS character counter
-SMS search
-Email threading
-Unified Email inbox
-Email archiving is now available when you setup Gmail
-Spell checker
-iPod music player can now create, edit and delete playlists
-5x digital zoom in still camera
-Touch-focus in video capture (for video enabled iPhones)
-Keyboard layouts span over QWERTY, QWERTZ, and AZERTY
-Minor icon design facelifts
-Video call support (only in iPhone 4 and only over Wi-Fi)
-iBooks e-book and PDF reader

What’s still missing:
-No Flash support in the web browser
-No true multitasking for all applications
-iOS4 for iPhone 3G has limited new feature set
-Poor performance on iPhone 3G
-No quick toggles for Wi-Fi, Bluetooth or 3G
-No social networking integration
-No info widgets on lockscreen or homescreen
-SMS tones are still not customizable
-No mass mark emails as read
-No proper file browser or access to the file system
-No USB mass storage mode
-No vibration feedback when touching the screen
-No Bluetooth file transfers to other mobile phones
-Contacts lack a swipe-to-delete or mass delete feature
-No SMS/MMS delivery notifications
-No smart dialing (but Spotlight is a somewhat of a substitute)
-No DivX or XviD video support and no official third-party application to play that
-The whole iPhone is too dependent on iTunes - you cannot add the same type of content (video, photos, apps) to the phone from two computers, a regular file management interface would have been much better

iOS4 review by GSMArena
http://www.gsmarena.com/apple_ios4-review-489.php