Apple has released its fifth-generation mobile operating system today, bringing more than 200 new features to the third and fourth-gen iPod touches, the iPhone 3GS, iPhone 4 and iPhone 4S, as well as the iPad and iPad 2. The overhaul is readily available in a 781MB download through iTunes (you'll need iTunes 10.5). We won't cover the full gamut in this post, but there are at least a dozen major changes worth highlighting:

Enhanced Wireless
Apple has effectively severed the ties between your mobile device and PC. Instead of connecting your iPhone to a computer for activation, iOS updates, backups and more, you can perform these tasks wirelessly. In that same vein, the update introduces the ability to wirelessly sync iOS 5 devices with your primary machine. You can also now use AirPlay over Apple TV to stream content from your mobile device to an HDTV.

Apple has developed its own messaging platform that allows iOS 5 users to send and receive content over Wi-Fi or 3G without paying for carrier texting services. iMessage has been added to the existing Messages app and supports text, pictures, videos, locations and contacts, as well as group messaging, the ability to track messages with delivery and read receipts, encryption, and the ability to see when someone is typing.

Notification Center
The notification system has been polished so alerts such as new email or texts are less annoying and easier to access. Rather than interrupt your session with a popup prompt, you're informed with a banner alert that disappears quickly. Notifications have also been centralized. They're displayed in a single location that you can access by swiping down from the top of any screen along with easy access from the Lock screen.

Camera, Photos, Twitter
The Camera is now more accessible with a shortcut on the Lock screen and easier to use courtesy of grid lines, pinch-to-zoom gestures, single-tap focus, exposure locks and the ability to take photos with the volume-up hardware button. You can tweak shots with the Photos app's new image editing features including crop, rotate, enhance and red-eye removal. It's also tied in with iCloud and the new Twitter app for quick sharing.

Newsstand, Safari
Along with centralized notifications, iOS 5 offers an app that organizes your magazine and newspaper app subscriptions. Besides letting you access your favorite publications in one location, Newsstand automatically updates new issues in the background. Safari also aims to improve your reading experience as it gains features to display Web articles without ads or clutter as well as a reading list to save interesting articles.

Reminders, Calendar, Mail
iOS 5 adds new to-do functionality via the Reminders app which, among other features, supports location-based alerts. The Mail app has received text formatting options, the ability to flag important messages, add and delete folders, and search a message's body. The Calendar app now lets you add, rename and delete calendars from your device, view attachments from inside the app, share schedules via iCloud and more.