NASA Released a Document last year asking all Countrys and Companys, who may land on the Moon in the future, to respect all the equipment laying on the Moons surface.
NASA is suggesting an exclusion zone of at least a 75 meter radius to all future Landers and Humans, to ensure that no dust is blown onto the working surfaces after their 40 years of continual working.
From a scientific perspective, many sites are still active (e.g., Apollo retro-reflectors), and continue to produce material, biological, and physical scientific data associated with long-term exposure of human-created systems to the lunar environment. NASA has also considered impacts to non-Apollo USG lunar artifacts.
There are five Lunar Sites with Laser Ranging Retro-Reflectors which are still used and working.
These are the Apollo 11, 14, and 15 sites, as well as the Soviet Lunokhod 1 and 2 Rover sites. These should be treated as special cases with approach mobility being tangential to the site. Once within a 10 m radius zone of the LRRR, mobility can only proceed at speeds that do not propel regolith particles in front and onto the various retroreflector sites.
Direct approach to the LRRR is not recommended.
Since these are active experimental stations, NASA prefers to not risk compromising or contaminating these activities through robotic visits. It should be noted that a physical disturbance would affect 40 years of LRRR data continuity.
The stability of the reflectors is critical to a variety of geophysical and relativistic physics problems. It is essential that these sites not be disturbed, however, careful observations of their current state would allow scientists a better idea of what is causing the slight degradation in the laser return signal. Which would help in designing the next generation of LRRRs.
There may be a slight degradation in the return signal over the years due to a layer of fine dust. Or even a physical warping of the Retroreflectors due to the constant heating of the suns rays, and extreme cold due to the Suns absence.
The dust may not be such a problem, because NASA knew from even before their first Lunar landing, that there would not be as much surface dust on the Moon, as people once believed.
They realised that almost all of the Dust in our space carries an Electrostatic Negative charge, therefore it would be more likely to be attracted to the Positive charged Earth, (as well as to Earths greater gravity attraction).
It is believed that the Earth aquires over 40,000 tons of Dust a year.....
(**Over the life of the Earth, I guestimate the Earth has doubled in size? Forgive me for adding that idea)
Yes I realise that we are losing weight in the form of gasses (air) every year....But the physical aquisition of Dust, over millions of years, would have made the Earths diameter Grow**
.....while the Moon, being a Negative body would tend repel a lot of the Negative dust that might otherwise be in the Moons path. This has been subsequently verified since 'local' incoming Space dust seems to aquire an Electrostatic charge from our Sun.
NASA would like to take Hi-Resolution photographs of all the historic Lunar equipment left up on the Moon, to enable a dust particle surface count to be made. But this may disturb the existing Data integrity.
It may be that some parts of the Moon aquire less Dust than other parts, (back of the Moon?).
Also the very fine Dust that is lying on the Moons surface can aquire an Eletrostatic charge, due to the action of the Sunlight in a vacuum.
It can and does then levitate, and float off, attracted elsewhere. There is the possibility that the static charge on the Dust may be modified by the areas rich in Helium3.
Future physical research, will give us more information.
The Moon rover Camera has found that most of the finer Dust is to be found around the top rim of the craters, it has visited.
The reason for this is not known.
www.lpi.usra.edu nssdc.gsfc.nasa.gov
ares.jsc.nasa.gov
www.osti.gov en.wikipedia.org
http://www.nasa.gov/pdf/617743main_NASA-USG_LUNAR_HISTORIC_SITES_RevA-508.pdf http://www.collectspace.com/news/news-102111a.html 
