The cw/ccw-screwing-gesture works pretty good, I think, already.
The problem is, it works only in microb but not in other applications (like in xterm, drawing, Fennec, ...)

When meego will have multitouch-gestures, the pinch-zoom-gesture will be the most used one. For running Meego-apps in N900 some gesture has to be mapped to pinch-gesture. The "tap and swipe" could be a good alternative to the cw/ccw-gesture.

(Or actually, I believe there is just "zoom-gesture" event received to the apps and the lower level GUI-system maps different kind of gestures to this "zoom-gesture"?)

With 3D-objects, "tap and swipe" could be much likely be rather 3D-rotation than zoom, because it can have the direction. cw/ccw-gesture works intuitively only on z-axis. With 3D, there has to be a way to distinguish translation-gesture from rotation-gesture. Simple swipe for translation, and tap-swipe for rotation would sound suitable.