Two weeks with iOS 4.0

As an iPhone developer, I've had my hands on the iOS 4.0 Gold Master for about two weeks on my 3GS. As it becomes publicly available, I'd like to share my subjective impressions of it.

Speed: iOS 4.0 feels faster. Period. I'm not sure if they lengthened the animations to make the transitions feel more dynamic, but the whole experience is favorable.

Mail: Multiple exchange accounts, email threading, a unified inbox, etc. It has made using my iPhone to keep track of 3-4 email accounts significantly easier to do.

Recently Used Apps List: If you double-click the home button, a dock will spring out of the bottom to show you your 4 most-recently-launched apps. The only down-side is that I haven't been able to find a way to configure the double-click to be anything else (I used to have it open my camera, for example). Perhaps the most useful aspect of this feature is that you can open this dock from within other apps, saving you a trip to the home screen.

iPod: Creating and editing playlists on the phone is a long overdue feature that I'm glad to finally have.

Folders: Drag one app icon onto another and they automatically form a folder. Folders are great with room for 12 apps per folder. Very well executed.

Camera: An update to the camera software has made even the 3GS's camera significantly faster. It feels like a whole new camera, and rivals many point-and-shoot cameras for speed.

Many of the other built-in apps like Safari and Maps seem generally faster and more responsive.

There are also a few features that I know about but have not able to test: Multitasking (there aren't any multitasking apps out yet), Game Center (the iPhone equivalent of xbox live, which is NOT going to be launched with iOS 4 this week), Tethering (I have not seen the service available from AT&T yet, though the configuration options exist on the phone), and iBooks (it did not ship with the GM).

Overall, Apple did a great job in making the iPhone experience generally feel faster and more fluid, even on the existing hardware. I imagine that with a hardware upgrade to the iPhone 4, that experience will only be heightened.