You might have spotted some of these screens in our thorough hands-on videos, but most of nuggets below are new discoveries. If you are playing with the iPhone OS 4 beta and notice some cool features we didn't spot, send a screenshot our way (to Rosa or Wilson), making sure to black out any embarrassing personal data, and we'll verify it and add it to this compilation.
Cellular Data On/Off You now have the option to toggle cellular data off.
SMS Character Count Guilty of running long on short messages? Now you can turn on a character count for SMS.
SMS Search Just as you can search your inbox, you can now search SMS messages.
Home Screen Backgrounds You can set separate backgrounds for your lock screen and home screen.
Camera Zoom By tapping the screen or sliding the little bar, you can zoom in and out when taking a picture.
Web and Wikipedia Search Can't find what you need on the phone? Jump to the web or Wikipedia straight from the global search screen.
Borderless Document View When screens are small to begin with, every millimetre counts. Document previews in the Mail app now eliminate pesky iPhone borders, giving you the most space you can get. (Still not much, but a marginal improvement.)
Streamlined "New Contact" Screen You can now enter more contact data without leaving the main screen. When you consider that every green plus signifies an annoying jump to another screen, you can easily see how much better it is now.
Events, Faces and Places in the Photo Menu If you are an iPhoto user, you can now sync pics to the iPhone (and iPad) via Events, Faces and Places, meaning less reliance on the artificial act of creating new albums.
Lyrics in iTunes While there are apps that do this already, the Lyrics option is kinda cool: Turn it on, and any lyrics that are pasted into the metadata of your iTunes tracks will show up automatically when you play those songs.
Spellcheck! Now, wherever you're typing, those little red underlines aren't far behind. Just remember that Apple's blind-eye-towards-profanity policy will certainly apply here, as it does with auto-correct.
Resize Photos While Sending This very cool time-saver pops up when you're emailing a photo, just after you hit "Send". Depending on how big the file is, you can have two to four size options, including "Actual Size".
New Playlists On-the-Go Playlists seem to be officially dead in iPhone OS 4, replaced by a more sensible "Add Playlist..." The benefit here is that you know it's something that will be synced back to iTunes, and you get to name it up front.
Art in Album View When you browse albums, and find one you like, you get more than just a list of tracks and a shuffle command. You get a little thumbnail of the album itself, and the length, track count and release date.
App-Specific Location Services By heading to Settings > Location Services, you'll be able to toggle which apps you're allowing to find your location and see which ones used the privilege recently based on the little compass arrow icon next to them.
Game Center There's not much that can be done in the Game Center right now, but one day it'll allow you to play against your friends, compete for high scores and earn achievements.
Email Threading You can set your email messages to thread.
Long Alpha-Numeric Passcodes No longer are you limited to guarding your precious data with four numbers! Now you can set longer, alphanumeric passcodes.
Unified Inbox You can view all your emails in one spot or segregate them to separate inboxes.
App Folders (with Alerts) A lot as been said about app folders, but did you know that if any alerts hit any apps inside a folder, the folder gets an exclamation point?