1) Safari has tabbed interface;
2) Camera uses side button;
3) Wizard like interface for setup;
4) Photo Stream auto uploads new photos to iCloud, downloads to all devices;
5) Newsstand feature allows you to download magazines.
6) New Messages, includes a Send Read Receipts setting (default off). A new Messages App was installed on my last iPad screen.
7) New Reminders feature. A new Reminders App was installed on my last iPad screen.
8) The new native Twitter App was installed over my previous one. It supports multiple Twitter accounts.
9) There is a Split Keyboard, but couldn't figure out how to get it to work.
A great lineup of features!
You should use your Mac or PC log-in to http://icloud.com to check out iCloud.
I didn't lose any data during upgrade but it took 2-3 hours including backup time.
Apple iOS 5 Features