Alfresco is quite cool. Last year they announced to provide support for Ubuntu means to provide packages for hardy - there was a news article from canonical and alfresco in august 2008.
As soon as this happens, I will try to build it with dab.
The other two: I do not know them but I will take a look on it. BTW, using the dab, anyone can build appliances for Proxmox VE
Is Debian an supported platform for Alfresco, what about OpenVZ? As it needs java, I assume it will need some special considerations to run as a OpenVZ container. maybe easier to run as KVM.
Turnkey Linux are working on an alfresco appliance.
Or another suggestion would be to package Gatein portal (http://www.jboss.org/gatein) with Alfresco in an appliance