Most of the features are already available in the unoffiicial App providers.
Apple just made if official.... but for others, this may be a start of wonderful things to come....
OS 4 will be available for Iphone 3GS, Ipad, Itouch new versions... sad to say the Iphone 3G and the old Itouch models do not support multitasking.
Still Apple is making a great deal of news on the net for this.... we'll have to wait for June, if it is worth the hype it's causing.
Still there are always alternatives..... don't forget to look at the bigger picture.