Suggesting that "Simple servers, such as DNS, DHCP, or Active Directory Servers" are going to be easy for virtualisation seems to me a bit strange. Anyone who has to live with the error rate inherent in having DHCP dynamically updating DNS with zones held in Active Directory will probably have written a "DNS-DHCP reconciliation tool" to fix the numerous discrepancies and concluded that this service collection is far from simple and maintenance free. Also, in many environments these are mission-critical services and putting the out in a cloud somewhere where you don't have instant control is maybe not such a good idea.

DHCP needs to be very fast and relkiable in some environments - if it's off at the far end of a slowish pipe it won't be useful, nor weill it if the pipe is unreliable. Same for Active Directory - particularly kerberos (user validation/login) and applying group policy (if I never again see event 1030 in a Windows system event log caused by network issues I'll be a happen man).

For the majority of people, a decision to virtualise the DHCP service is clearly a manifestation of CTD in a non-database sphere! How much server power will you save? How much network cost will you incur? I don't think there's any saving to be made, in fact I'm pretty sure that it would be a pointless and expensive exercise.

The real barrier isn't porting ones own proprietary applications into the cloud - it's coping with poorly written software provided by third parties. Getting one's own application structure cleaner and more hardware independent is something that's good to do anyway (it gives us some extra flexibility and future-proofing) so the need for that is not the real barrier.