I have just worked out how to set up new desktop activities in kde4. I can switch between the activities using the activity widget. However the activity widget does not work well.

If I have the widget on the panel then it takes up far too much room. If I have it on the desktop then I need a widget on each activity desktop. This shows the button that was last pressed on that widget, not the global state of the activities. For instance if I am in Activity1 and click activity2 I go to activity2. When I go back to activity1 the activity2 button is still highlighted and to go back to activity2 I have to click on activity1 and then again on activity2.

There are supposed to be shortcuts to switch among activities. But the ones from the Plasma handbook didn't work when I tested it.
Ctrl+[
Ctrl+]

It may depend on the version of KDE4 you have.

What I have done is create a small panel at the top with the activity widget on it. That seems to work OK.

By the way, if you don't use activities, you can change from "Desktop" to "Plain Desktop" to make the Cashew in the corner go away.

I just went the other way on my netbook.

I just upgraded from KDE 4.1 to 4.3. There is an "Activity Bar" widget you can use to easily switch between activities.

We know that. It is the wy that it works which was the problem but which I think I have solved.