As previously discussed here, Asymmetric Disk Only Quorum is a feature of Windows Server 2008 Clustering that is now officially supported by Microsoft. Asymmetric Disk Only Quorum allows a multisubnet cluster to use a Disk Only quorum model, even though some nodes cannot see the storage of that disk resource.
Microsoft has now released updated quorum documentation that shows the support for this feature: http://technet.microsoft.com/en-us/library/cc770620(WS.10).aspx
David P. Smith 