I was able to successfully insert a new document using the following code but I was not able to get the _id of the newly inserted document.
After the insert, user is null. Thank you!
MongoServer server = MongoServer.Create();
MongoDatabase test = server.GetDatabase("Test");
MongoCollection<BsonDocument> users = test.GetCollection("Users");
BsonDocument user = new BsonDocument();
user.Add("FirstName", "John");
user.Add("LastName", "Michael");
user.Add("Address", "123 Main Street");
user.Add("City", "Newport Beach");
user.Add("State", "CA");
user.Add("ZipCode", "92660");
user.Add("Email", "John.Michael@myemail.com");
user.Add("CreatedDate", DateTime.Now);
user.Add("IPAddress", "10.1.1.1");
user = users.Save(user);
string idSTring = user["_id"].ToString().Replace("\"", "");