Just wanted to say thanks to @mahfiaz for noting that it's possible to use the XML editor - worked for me in inkscape 0.48.1; note that with two open documents, there is still only one XML editor, which changes its contents depending on which document window has focus; only Ctrl-C does copying in XML editor, and there is no feedback - and finally the trickiest: when you paste the layer node in the target document, if you have nothing selected in the XML editor - or if you have the root selected, then nothing will be pasted in the target doc upon Ctrl-V! What one needs to do, is to select an actual group node before Ctrl-V pasting - while that may imply that the layer will be pasted as a child of the selected group node, it won't - it will be properly pasted as a child of root. Note also that upon successful paste, some sort of a transform is added to the pasted layer node - that can be just deleted as an attribute from the XML editor, and the layer will be shown as it was in the source document (provided source and target document are the same size)
Just wanted to say thanks to @mahfiaz for noting that it's possible to use the XML editor - worked for me in inkscape 0.48.1; note that with two open documents, there is still only one XML editor, which changes its contents depending on which document window has focus; only Ctrl-C does copying in XML editor, and there is no feedback - and finally the trickiest: when you paste the layer node in the target document, if you have nothing selected in the XML editor - or if you have the root selected, then nothing will be pasted in the target doc upon Ctrl-V! What one needs to do, is to select an actual group node before Ctrl-V pasting - while that may imply that the layer will be pasted as a child of the selected group node, it won't - it will be properly pasted as a child of root. Note also that upon successful paste, some sort of a transform is added to the pasted layer node - that can be just deleted as an attribute from the XML editor, and the layer will be shown as it was in the source document (provided source and target document are the same size)