Gary Lapointe recently released a custom STSADM command for setting the BackConnectionHostNames registry key. The relevant Microsoft KB article recommends specifying each host header with the BackConnectionHostNames key rather than disabling the loopback check, as this check is a valuable security fix. As Gary Lapointe mentions, Spencer Harbar put together some thorough background information on the roots of the fix. Without this command, setup and maintenance can be a bit of a hassle if you have lots of SharePoint applications or lots of Alternate Access Mappings (or if any of this information changes with any regularity). These registry changes need to be made on each web server for any sites with host headers. This includes Central Administration if it’s not configured on <servername:port>. So this could get quite laborious if the farm is fairly large. The UpdateFarm parameter may be particularly helpful in this regard.