Drag and drop

Has anyone implemented a real-time drag&drop system?
The most important thing is to transform mouse coordinates (in 2D viewport) to 3D (world) coordinates. I’ve tried some matrix-based methods but without success.
Has anyone a sample .blend file that illustrates this?
Thank you

you mean like click and drag?

I made a demo with boxes with that, controlled the cursor with keyboard and no python, pretty shitty though, besides I lost the file

scabootsca did.
look in http://blenderartists.org/forum/showpost.php?p=797198&postcount=8