I think it's a good idea.  When you have a lot of modules on the page it's always good to automatically bring areas you are working with into focus.  However, there are a lot of people that find that feature very frustrating.

I think it just needs to evolve a bit.  If there is only one module on the page then the dimming should be disabled.  If there are multiple modules on the page then allow the dim to engage but only if you mouse into another module.  It might also be a good idea to track the rate of mouse movement before engaging so that you don't switch the dim between content areas when the user is just moving the mouse up to the DNN Control panel or to a skin object that is on the page for development.

I think that would improve the feature so that it isn't frustrating for people.