Last week was a big week for Apple. In addition to releasing the iPhone 4S, Apple also came out with the iOS 5, its new mobile operating system that works with not only the 4S, but the iPhone 4 and 3GS, as well as the iPod touch and the iPad.  I recently upgraded my iPhone 3GS to the new operating system this weekend, and here's a few of the many new features that are worth mentioning:

The Notification Center is one of the more convenient features. By simply dragging your finger vertically down the screen, you'll bring up this feature which keeps all of your texts, E-mail and other notifications in one place, along with a built-in weather forecast and stock ticker. You can see all your messages at a glance without having to open up all those apps. And speaking of messages, I particularly like how new messages in iOS 5 appear in a small, unobtrusive box at the top of the screen, as opposed to that giant blue box that got in the way of whatever you were doing.

Another handy feature is the Reminders app, a built-in to-do list. Just enter in your reminder ("Pick up a gallon of milk," for example) and your iPhone will remind you either on a specific date, or when you arrive at a specific location.

If you one of those who has multiple Apple devices, iMessage may serve you well. This new messaging service allows you to send unlimited text message to anyone who has an iPhone, iPad or iPod Touch. It allow lets you start an iOS conversation on one device, then continue it on another device. So if you start messaging your friend on an iPad, you can keep that conversation going on your iPhone. For someone who's always keeping in touch with their friends, like me, this is a really cool feature.

If you like to read on your Apple devices, you might want to check out the Newsstand app. This app keeps all of your e-magazine subscriptions  (like the Wall Street Journal, Popular Science, Cosmopolitan, etc.) in one place. It also automatically updates when a new issue is released. You can purchase new magazines and newspapers form the App Store. However, although it says "Free" in the App Store, you will be charged a subscription fee for those magazines if you want to continue reading them, so keep that in mind.

If you haven't upgraded to iOS 5 yet, all you need to do is plug your device into iTunes and follow the on-screen prompts. It will take anywhere between 30 minutes to an hour to complete the upgrade, but it's completely free of charge, and well worth the time.