It may not be as applicable to Blackhawk, being a private, membership only facility, but I think the most important things for any mountain bike trail system website is a good map and current trail conditions. Both of which should be easily found and accessible.
Our family has planned vacations for the last several years around mountain biking. It is amazing how many of the "must go" trail systems have terrible maps, no current status on trail conditions, or it is extremely difficult to locate the information. When trying to plan a trip to far off locations, not being able to easily access this information is incredibly frustrating. In more than one case for us, this alone has led me to eliminate certain areas from consideration.
On this note, I think CORP does an exceptional job on this front, perhaps I've been spoiled.
