Is your network in healthy state?
When was the last time you cleaned up stale domain controller records in Active Directory? Are scavenging intervals set correctly for all DNS zones? Does Exchange recipient policies use supported SMTP address format? Did you ever read critical SAM event logs?
Even though you know how many different things you need to check, do you have time do go through the list periodically? Or do you learn that things stopped working by increasing number of phone calls?
Windows Essential Business Server (a.k.a. EBS) offers a free diagnosis tool called Preparation and Planning Wizards for IT Administrators. The wizard runs a number of checks on your network and generates a network health report without changing any settings you made. Let me tell the good news: You don't have to buy EBS or pay anything to anybody. This small and simple wizard generates a detailed report for free. Free as in beer! Give this wizard a shot and it will tell you what kind of problems your network has. Download it today: http://www.microsoft.com/downloads/details.aspx?FamilyId=E3906025-00E3-407D-BF5B-99D546021923
Free software from Microsoft in this bad economic situation: Sweet deal! Sweet as in donuts.