Steve Jobs unveiled iOS 5 back at WWDC this year. Since then, those of us with an iPhone 3GS or later device have been anxiously looking forward to the array of new features and functionality introduced in the update. At last week's Let's Talk iPhone keynote, Apple revealed that today was the lucky day for iOS 5, and if you've got a device that'll run it� Plug it into iTunes, make sure you sync, and mash that update button.

My favorite improvement so far has definitely got to be the entirely revised push alert notification system. That nasty blue popup that interrupts everything you're doing when you get a text message, your Tiny Tower is ready for something, or the zillion other things that used that type of been notification is a thing of the past. Now there's an incredibly elegant notification center where all these alerts are stored, and the actual popups themselves simply scroll in from the top instead of stealing focus.

If you've got an iPad 2 (or are getting an iPhone 4S in a few days), you'll be able to do display mirroring via AirPlay. Doing cool things with this is largely dependent on developers utilizing it in interesting ways, but so far Firemint is doing awesome things with Real Racing 2.

In addition, Game Center has seen a few tweaks. One I'm most excited for is turn-based support. If developers utilize it, Game Center can handle all of the matchmaking and turn data management between players. I've heard from developers that this functionality does not degrade gracefully to previous versions of iOS, but once iOS 5 adoption picks up we could see a rush of great turn-based games now that developers can offload their entire online infrastructure onto Game Center.

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iCloud isn't something that should be underestimated. Out of the box it'll keep your device backed up to Apple's data centers and in the event of device failure, loss, theft, or whatever else you'll be able to re-download the entire contents of your phone regardless of the last time you synced. Also, once developers start embracing it, you'll be able to seamlessly sync save game data between devices. As someone who often plays games on both my iPhone and iPad, I can't wait for this to pick up steam.

iOS 5 is an incredible upgrade. I've been running the developer version since the gold master hit last week, and much like the upgrade from iOS 3 to iOS 4, my iPhone 4 feels like a totally new device. iOS 5 boasts a feature list of over 200 additions and improvements, so if you want to know everything that is new and different, check out this huge list over on MacRumors.