Use Keyboard Cover?

A keyboard cover may stop the lid from closing properly (not entirely sure tho as I don't on a rMB), however I don't imagine it would damage it. If you are worried about the cover leaving marks on the screen you could also purchase a screen protector.

http://www.macinfo.us/should-you-buy-a-keyboard-protector-for-your-mac.php

 

You can use one but there are two important factors to remember

1, your adding an insulating layer
2, you must remove it before closing your MacBook or risk damaging the hinges.

 

Potentially yes there is no space between the screen and the keys when it's closed

 

I used a keyboard cover on my rMBP but I'm going without this time around on my rMB. Since the keys are more recessed I [personally] feel like there is less space for stuff to fall into as there also seems to be less space around the keys. As well the cover made the keys much more "mushy" on the rMBP so even though I really enjoy the stock keyboard, my need to keep it pristine made for a poorer experience than if I went without.

I did not remove the cover on the rMBP when I closed the machine for a good long time and eventually it started leaving crap on the screen as well, so I started to remove it afterwards. Thus far it doesn't seem to have negatively affected the hinge but I suppose that could be a possibility if continued down the road.

Think I'm just going to keep foods and liquids away from the machine to avoid the possibility of spillage rather than go with a cover this time 'round.