I have noticed a significant speed reduction in AutoCAD 2010 products when the Layer Properties palette is open vs. when it is closed. At first I told my users to turn if off when not in use. Yeah, I can't even I remember every time. The solution (or work around) for now is replacing the the layer command with Classiclayer. Classiclayer brings up old reliable; the Layer Properties Manager dialog box. There is no way to leave it open, it's a dialog not a palette.
If you really lock things down, you can redfine the layer command. For me it works just as well to change the macro in the CUI and change the PGP for LA if you have that kind of control.