An overlooked command from AutoCAD LT 2008 is Set By Layer. In LT 2010, you'll find it on the Modify panel of the home tab.
It does just what you think it might -- changes the color, linetype, and lineweight of all selected objects to ByLayer (from whatver it was).
It's a great command, because it makes changing object properties quick and easy -- and once everything's back to ByLayer, you can change the layer color and know that all objects will update.
Even better, it works on blocks too, so that all the objects in the block reflect the layer properties.
There's also a settings option so that you can choose which object properties are modified by Set By Layer.
This tip will have to last you for a little while -- Autodesk is going on vacation next week, so by extension the blog will be on vacation too. Feel free to come by and browse the archives other good tips, but new content won't return until July 6th. Happy 4th of July to my US readers!