Example
Drag media file onto Totem's playlist to enqueue
Bug in Compiz
Especially for Unity (formerly Netbook Edition, being intended for small screens) this is quite a vital feature, as applications most often are run fullscreen, and dragging with the touchpad can be cumbersome.
https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/624810
Any hint on where to start fixing the bug? Which file/line in compiz source code?
Usability background
According to Fitts, Accot, and Zhai, the time required to rapidly move to a target area is a function of the distance to and the size of the target (cf. Fitts's law and Steering law).
Drag'n'Drop without Alt-Tab across fullscreen windows requires
- start to drag object
- move to launcher/taskbar
- steer to target app icon -- small and distant target!
- wait for app to become focused
- steer onto window -- (huge target)
optionally: steer onto intended area of window, e.g. playlist (fairly large target) - drop object
Drag'n'Drop with Alt-Tab on the other hand only requires
- start to drag object
- Alt-Tab to other app
optionally: steer onto intended area of window, e.g. playlist (fairly large target) - drop object
Thus, no small and distant target required for Drag'n'Drop whilst Alt-tabbing
Workarounds
Interesting and probably for many users useful alternative approaches are presented in the answers below. Great many thanks to the community!
Correct answer
... seems to be available only when the bug is fixed, though.
Some more recent action, maybe relevant as related bug: https://bugs.launchpad.net/ayatana-design/+bug/727903