I originally hand-picked the KDE packages when I installed it here (4.6.5 in sid). Some I installed with recommends, some not and IIRC I generally avoided meta-packages. After the 4.7.4 upgrade I had a look in this activities 'thing' :) When first activating the 'Search and Launch' and the 'Desktop Icons' activities they would show a little garbled window about the apps that were supposed to be run automatically (and 'S&L' didn't work). This was fixed by installing plasma-netbook. plasma-netbook is so tiny and needed by the activities that I think it should become a dependency of kde-plasma-desktop.