Yes, they're a little late to the party (Steve Jobs even admitted as such), but the day has finally come that you no longer need to jailbreak your iPhone or iPod Touch just to get multiple applications running at the same time. Apart from just allowing you to run multiple applications side-by-side, Apple will provide several APIs for developers to tap into, which allows applications to become multitasking aware; for instance, TomTom spoken directions while playing music, or Pandora music controls on the lock screen.
The interface for managing multiple running applications is relatively straightforward; pressing the Home button twice pulls up a dock from the bottom of the screen containing the icons of currently running applications. Apple also added an API for applications to save their state when they quit, and return right to where you started when you re-open them. As expected, multitasking will not be available on the iPhone 3G and second generation iPod Touch (they simply lack the power).
Another tentpole is a revamped email client. Taking cues from the competition, Apple has finally implemented a unified inbox, and you can now have multiple Exchange accounts. A threaded view has been added to Mail as well, which will certainly be a welcome addition for many (I never got the point, but hey, I'm weird).
Another major new feature is Folders. The iPhone has always been extremely clumsy when it came to managing all the icons on your home screens, making it hard to find the applications you needed. iPhone OS 4.0 will add the ability to create folders on the home screens. You can simply drag an application onto another, and it will automatically create a folder (which you can name). Tapping on that folder will open a pop-up displaying its contents. I am very, very, very happy my iPhone will get this feature. I'm not kidding.
Apple will also launch iBooks on the iPhone, which basically looks like a miniature version of iBooks on the iPad. Books you bought will appear across all devices, so you don't have to fiddle with that. There are also several new enterprise features which should make the device more interesting in that setting (I'm not particularly well versed in that world, so I'll just take their word for it).
The two remaining tentpoles are big ones. First, there's Game Kit. It can best be described as Xbox Live for the iPhone - with the difference that this will arrive coming summer, while the actual mobile Xbox Live will arrive much later with Windows Phone 7. Game Kit will bring, among other things, achievements and leader boards.
Then there's the seventh and final tentpole - the expected iAd mobile ad network. This really is a big one. The entire iAd portion of the presentation was a big middle finger towards Google and Adobe - there's no other way to describe it. And you have to hand it to Apple; iAd looks pretty darn impressive.
Jobs lamented current ads in applications that yank you out of your application straight to an advertiser's web page. Apple's idea is different: the advertisement is completely interactive, and you remain within the application. You can embed videos, games, and a whole load of other things. It's a bit difficult to describe, so here's an example: Jobs showed an ad for Toy Story 3, and from within the ad, you could use the location framework to find a nearby cinema which plays the film.
Jobs reiterated the ads are made using HTML5 (the finger to Adobe), while also being clear to mention that search has not happened on phones; applications have (the finger to Google). Rest assured that at the end of the year, iAd's competitors can close up shop when it comes to the iPhone. Oh, Apple delivers a 60/40 split, with developers taking the 60.
iPhone OS 4.0 will be delivered to the iPhone 3GS and third generation iPod Touch this summer, while the iPad version will hit in autumn.
I have to say - I'm impressed, and I can't wait for version 4.0 to hit my iPhone. While I'm particularly interested in multitasking, Folders are a very welcome addition as well. I am disappointed, though, that we'll still be stuck with those archaic and annoying modal dialogs (no new notification system) and there won't be a proper home screen, either.
Overall, it looks like a very worthwhile upgrade that takes some of Android, some of webOS, some of the jailbreak community, stirs it a little, and calls it version 4.0.