The iPhone OS 4.0 announcement just wound down, and as expected, there were a LOT of welcome additions/enhancements.
The biggest (and most highly anticipated) upgrade: MULTITASKING! Apple has promised that OS 4.0's multitasking will work with third-party apps and WON'T drain the battery (an issue plaguing both Palm Pre and Nexus One users). Thanks to a customized audio API, streaming-music apps like Pandora will continue to play when shuffled to the background, and even display a controller icon on the lock screen. Other features benefitting from multitasking include background GPS turn-by-turn prompts (even under music!) and the ability of VOIP apps like Skype to receive incoming calls in the background and pop up a prompt to accept or ignore the call.
(Caveat emptor: this is not "true" fulltime multitasking, but selectively granted to certain processes that would really benefit from it such as audio, GPS, and VOIP.)
Another major interface enhancement is the ability to create folders of apps, merely by stacking two or more apps on top of one another. With folders, the amount of apps available on the desktop jumps from 180 to over 2000.
On the email front, OS 4.0 debuts the unified in-box approach that Apple knows and loves. There's also support for multiple Exchange accounts, fast inbox switching, and the abilities to organize messages by thread and open attachments in their associated app. The Exchange improvements also tie in with improvements to the enterprise experience: better data protection, mobile device management, wireless app distribution, support for Exchange Server 2010, and new VPN options.
iBooks was one of the big selling points of the recent iPad launch, and now iPhone users get the same ereader access. On the gaming front, OS 4.0 is not only gunning for the DS/PSP handheld game market, but has the console world in their crosshairs as they prepare to roll out their own social gaming network. And Apple is now officially getting into the mobile advertising hottub with iAds: a way to deliver rich-content commercials within an app without actually exiting said app.
(And that doesn't even include goodies like Bluetooth keyboard support, or the over 1500 new APIs to allow devs to access the calendar, photo library, or QuickLook…)
In one sense, OS 4.0 is a big, hearty middle finger to the jailbreak community, as it now incorporates features (multitasking, folders) previously available only through pwnage. Likewise, Apple made it very clear that until they licked the battery-drain issue, multitasking would not become a reality. At the same time, multitasking is still not all-embracing: IM and Twitter won't have access to background notifications, and will still have to rely on push technology. All things considered, though, this is a MAJOR, major upgrade that plenty of iPhone owners will happily adopt.