I did some digging once I saw this thread as I am looking for near-by places to go wheeling. NEMBA (New England Mountain Biking Assoc) bought the property. Some quotes from their FAQ's...
http://www.nemba.org/Articles/Vietnam/NEMBAsVietnamProperty.html
As most of you in the mountain bike community know, in the fall of 2003, NEMBA accomplished the incredible feat of being the first mountain bike group in history to purchase and own property by buying 47 acres in the area commonly referred to as “Vietnam.” This parcel of land has been designated for use by all traditional non-motorized vehicles.
After the land purchase, NEMBA established a Land Management Committee to focus on the area. The committee is tackling all concerns regarding this property and welcomes your suggestions.
Presently, the committee is focused on establishing short and long term goals for managing the property. The number one short term goal has been to work political issues with the Holliston and Milford Conservation Committees and establish ourselves as “good neighbors.” Among our other goals are to improve trails while respecting natural surroundings and maintaining challenging terrain. This is all designed to provide full enjoyment of our area. Please respect this area and our neighbors in order for future riders to enjoy it for years to come.
What about motorized vehicles?
Access by motor vehicle is not allowed on NEMBA land and is also prohibited on all other land in the “Vietnam” area. There is presently a major crackdown on motorized vehicles occurring in the town of Milford. NEMBA recently purchased a number of “No motorized vehicles” signs, and you should see them installed very soon.
How much land does NEMBA own?
The NEMBA parcel is 47 acres in Milford only. The parcel is surrounded by approximately 1000 acres extending to Holliston, Hopkinton, and private lands.