iOS4 Update is now available for download. Apple users just open iTunes and sync iPhone and download process will begin.
For a complete, comprehensive walkthrough of iOS4 and how the new features work the following guide is excellent and includes user videos of the different features. http://www.tipb.com/2010/06/14/ios-4-walkthrough/
I guess it is neat I'm concerned that the aps will multitask too much and slow it down because I won't close them completely.
All lot of hidden features have been compiled by the good people of Gizmodo: 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 millimeter 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/Podcast Data Toggle UPDATED: Though viewing lyrics you pasted into iTunes (or podcast data) on your iPod Touch or iPhone can be fun, apparently some people wanted to be able to turn it on or off globally. Now there's a toggle. Happy? 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 for Lock Screens No longer are you limited to guarding your precious data with four numbers! Now you can set longer, alphanumeric passcodes for your lock screen. 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? Contact Pictures in Emails If you receive an email from a person who has a picture in your contacts, you'll now see a tiny image of him or her in the corner. Folders in the Dock It's not surprising, but it's good to know that you can in fact stick folders into the dock. Closing Apps Curiously enough, it's possible to actually close apps from the app tray. All you do is hold down an icon—just as if you're trying to delete it—and wait for the minus sign to pop up. A Shiny New Calculator Icon It's not a crazy feature, but the calculator icon does look a bit different now—same old calculator app though. Birthday Calendar There's a birthday calendar—which you can toggle off—which compiles all the birthdays from your contacts. Smart Links For Dates and Addresses in Emails Addresses and dates in emails now turn into links which can be used to look up the locations or add the dates as events. This is similar to what you see in the Gmail web client. Double-Tap and Hold Brings Up Phone Favorites Not our favorite hidden secret, the beloved Phone Favorites shortcut has been demoted. Instead of the double tap—which now brings up the task manager—you have to double-tap and hold. Single-tap holding of course triggers Voice Control. Now, what the hell happened to double-tap for iPod controls? Anyone know? Apparently double-tapping the home button when music is playing will still bring up the iPod controls when the screen is locked. Bluetooth Keyboard Pairing You can now pair your Apple bluetooth keyboard with your iPhone. Failed SMS Notification In the past, you wouldn't be aware if an SMS failed to send until you actually checked in the message screen. Now you get a lovely little exclamation mark to notify you that something went wrong. Note Syncing Hello! There's now a toggle allowing you to turn on sync for notes. In-Page Video Playback in Mobile Safari Instead of bumping you to a QuickTime mini app every time you stumble upon compatible video, the new iPhone Safari browser does what the iPad does, and shows you the video right there on the page. If you want to go full screen, you give it a tap. It's your choice now. Vertical YouTube You can finally watch YouTube videos in a vertical orientation. Keyboard Layouts You can switch to your preferred type of keyboard layout.
That'll only be an issue if you're running multiple background processes - Pandora + a GPS tracker, for instance. Normal apps are essentially paused, freeze-dried, compressed, and restored as needed.
