It seems Microsoft have ditched the ability to use a parallel SCSI device as a shared disk resource in Windows Server 2008 failover clusters, which now require a SAS, FC or iSCSI LUN for the job.
I have yet to work somewhere that clustered a lot of VMs, but potentially this and the 'one physical node / one virtual node' are not possible anymore with 2008 unless you have iSCSI available. Coincidentally perhaps, I have also yet to work somewhere with a lot of iSCSI deployed :-)
I haven't tried it in ESX (yet) but the Windows Server 2008 cluster validation wizard fails with a Workstation 6 based cluster. If anyone else out there knows / tests it out before me, let me know!
UPDATE: As expected, it doesn't work on ESX either. Wonder if it will work on Hyper-V...