Today is the day folks. iOS 5, iCloud, and iTunes 10.5 are all arriving. You can finally take advantage of those 5 free gigabytes of storage from Apple! Additionally, the iPhone now has some nifty new camera features like native editing, Twitter sharing, and quick access to the camera app via the lock screen (when you double tap the home button on the lock screen).
Also, there is iMessage, which is very similar to BBM. You can text, send photos/video, and share contacts for free with other iOS 5 users. Another nifty feature is Reminders, which allows you to create to do lists on the go.
The biggest feature in my eyes is the notification center. Drag down from the top to reveal widgets for the weather and stock market as well as notifications from text messages and other apps. This is a feature that Android users have held over the heads of iOS fans for some time now. It makes things easy to ready and get to.
Make sure you do a back up of your iOS device and go update right now!