I updated iOS4.3 before Itunes 10.2.1

What changes are you looking for?
They are very minimal changes visually.
Here is what has changed:

http://www.apple.com/ios/

No, you don't have to "activate' anything, but may have to turn on some features.

What have you done to check new functionality?

If you were on 4.2 before then the changes are fairly minor (more like enhancements rather than new features), and are listed here http://www.apple.com/ios/. One of the noticeable new features is the ability to now set what teh switch on the right hand side of the iPad does : rotation lock or mute notifications - +Settings > General > Use Side Switch to+

The other 'major' change is the ability is to Home Share i.e. play music/vidos from your computer's iTunes library on your iPad :

1, enable Home Sharing on iTunes on your computer (under the Advanced menu)
2, on your iPad :Settngs > iPod - type in your iTunes account and password
3, you should get a house icon in the top left of your iTunes app; select that and you should see your computer's iTunes library.

Message was edited by: King_Penguin

Nope there is no multitasking option as you describe.
Did you look at what I posted about what the update included?

If you are thinking of gestures, then they didn't make it into the final release