yahoo!! recently i have found out how to improve the SLA to customer by enable HTTP health Monitor at our BigIp pool TTP health Monitor at our BigIp pool .
if you have BIG-IP® LOCAL TRAFFIC MANAGER then you can create the HTTP health Monitor to monitor your MOSS2007. This will help to monitor your MOSS site , if discover one your web front end server is not respond on the IIS between the timeout you set then big ip will not send any request from user to this server. So user will not impacted by that server :)
below have more information you can refer to how to set it :
setup F5 with MOSS 2007