Labels are not visible in the 3D view.
If you want to display some text in the 3D view, you can use an imaging program to create an image with that text, then save it at PNG format with transparency, and apply that image/text texture to a very thin box.
I agree it's not convenient but as the attached example shows, it works correctly.
----------------------------------------
Bedroom.png
(911 bytes)
(Download count: 1942)
(Text displayed in the 3D view)----------------------------------------
BedroomWith3DText.sh3d
(20149 bytes)
(Download count: 375)
(Text displayed in the 3D view)----------------------------------------
Emmanuel Puybaret, Sweet Home 3D creator
