How do I move applications between KDE Activities?

Ok first you want to open your activities (SUPER ( Windows )+Q) unlock widgets, and create at least one other activity. Make sure that more than one of the activities are not stopped (e.g. red X).

*(note: Remember the activity that is highlighted is the currently active one, and according to aseigo only one can be active at a time, though I haven't found this to be exactly true.)

Now right click on the title bar of the window you want to associate with an activity. Go to Activities, and select the activity you want it to be associated with. Please note this dialog is only present if the there are other activites in "not stopped state:" if you stop all but one it won't show the activities dialog. Stopped activities are not shown in this dialog.

note: only works in 4.6 (or later? activities have changed much over kde 4's lifetime, I actually don't know if they'll work this way in 4.7, I honestly hope they don't, this is not intuitive)