Yep, the order can matter a lot. Sometimes DNS servers go down, and managers are supposed to be ready for this by having secondary, even tertiary servers ready. Alas, this is not always the case-the back ups are not always ready, and the customers get no pages. Explicitly entering a second (if not secondary)server is one way to be ready for that. When the primary server is down but doesn't know it then you have real problems! Switching the second listed server to the top of the list can solve this, and a number of other issues.