Now that I have had chance to play more with the multitasking feature implemented in iOS4 I can honestly say that a) I like it and b) it works very well.  

This morning I needed to browse a website and, using the information on there as reference, edit an SMS.  Being able to quickly switch between the two and rejoining each application in exactly the same state/place as I left it worked perfectly.  Switching between the two applications was very quick and, thanks to Apple’s brilliant attention to detail and user experience, the switch between the two was very fluid, with a great animation of the application sliding to the front from behind the current application.

More applications are being updated now with iOS4 support so the full benefits of multitasking will soon be much more evident.

Would I change anything?

Yes.  I would like an option to “kill all” open applications so that I don’t have to close each one individually.  I don’t like to leave apps running indefinitely so am forever closing them down at some point.  If I leave it a while, I end up closing several apps one at a time.  A “kill all running apps” option would be most welcome.