Civil 3D 2011 Service Pack 2 installed:
New drawing, nothing else open. New drawing using C3D "_AutoCAD Civil 3D (Imperial) NCS.dwt"
Draw a line, right click properties (About a second to load window)
Click on Layer box, dropdown appears
Click on a new layer name (Nothing happens at first, have to wait between 3-5 seconds each time for change to take effect) ...This is true for other properties, such as color, linetype, lineweight, etc. and same case for C3D specific object data editing.
System: XP Pro 32 bit, 3.06 Ghz Core2, 4GB Ram (2+ GB available at time of test), NVidia Quadro FX2700M