Currently if you want to move a selected layer (or multiple layers) from one open PSD to another, you have to:
1. Select the layer(s) in the Layers palette.
2. Click the Move Tool (if not already active).
3. Make sure the "Auto-Select" feature isn't on.
4. Click within the canvas.
5. Drag to the new PSD.
While that's not a HUGE deal, I am still not sure why we can't just omit steps 2 through 4. We should be able to select the Layers in the palette, and then drag them to the new document (either the new document's canvas area, or the new document's layer palette).
Speaking of the latter, with the way things currently work, when I drag layers from one PSD into another, the layers palette doesn't get updated to the document I'm currently dragging it into. If I have 5 PSDs open and they all look the exact same, but the layer structures are actually different (but I don't remember the file name), I have no way of knowing if I am in the right PSD or not. In short, the layer palette should update to the currect one, depending on what document/tab I am about to drag/release my layers into.