Joshua Nozzi: Your Very Own Drag Show with JLNDragEffectManager

"Cocoa developers were treated to a nice Interface Builder makeover in version 3. One effect we’ve all been admiring is dragging an item from the Library palette onto a window. It’s actually not too hard and just takes a little showmanship. I’ll show you how it’s done."

I played with it a little bit this evening. It's pretty easy to use.