By default, Small Business Server 2008 uses “Root Hints” to resolve DNS Queries for External (Internet) Hosts. Previous versions of SBS were configured to forward Queries to a third party server (normally at the ISP). In my experience, this mechanism for using “Root Hints” has proven to be slow and unreliable, so I prefer to set up my SBS to use the more traditional method of referring DNS Queries to an external server.
OpenDNS is “Free” Service that has proved to be extremely fast and reliable. It has the additional benefit of providing content filtering. A very simple tutorial for configuring 2008 Server is here
IMPORTANT NOTE: Do NOT change the DNS Settings on the NIC of your Small Business Server. These should always point back to the IP Address of the SBS (and not to an external DNS such as OpenDNS or your ISP).