In addition to the iPhone 4S, which clearly stole the show, Apple used its October 4 event to officially launch iOS 5 for iPhone, iPad, and the iPod touch and iCloud.

Unlike the iPhone 4S, which is only an incremental update, iOS 5 is a major upgrade that changes the complexion of Apple’s mobile OS and adds a number of new features.

Most notable new iOS 5 features:

Notification Center — Track new email, texts, friend requests, and more in one convenient location
iMessage — Send unlimited text messages via Wi-Fi or 3G from your iPad, iPhone, or iPod touch to other iOS devices
Newsstand — Lets you access your favorite publications which can be purchased from the App Store
Reminders — To-do lists with due dates and locations
PC Free — Over-The-Air activation, updates, and syncing
Camera — Available from the lock screen, use the volume button as the shutter release
Photos — Crop, rotate, enhance, and remove red-eye directly in app
Safari — with Reading List and tabs on the iPad
Other notable features in iOS 5 include:

Siri, voice-driven “Intelligent Assistant” (Currently in beta, iPhone 4S only)
Task syncing
System-level dictionary support
iPad keyboard improvements
Enhanced gesture support
Some will be nonplussed by the iOS 5 and iCloud announcements, because they debuted at WWDC11 in June, 2011.

iOS 5 is compatible with the iPhone 3GS, iPhone 4, iPhone 4S, iPod touch (third and fourth generation), and the iPad and iPad 2 but not all features will be available for all devices. iOS 5 will unify all compatible devices to the same version of the OS for the first time since iOS 3.1. More information on iOS 5’s features can be found on the Apple website.

In addition to iOS 5, Apple also officially announced its iCloud service, a cloud storage, syncing and backup service that’s tightly integrated into the new version of iOS and OS X Lion. iCloud replaces MobileMe (which is going away in June 2012) and automatically syncs music, documents, and photos between all your devices.

Sadly, Apple didn’t announce a replacement for its MobileMe Gallery, hastening my migration Picasa Web albums.

iOS 5 and iCloud will be available on October 12, 2011