It is recommended to enable Datacenter Activation Coordination (DAC) mode for Exchange database availability groups that meet the criteria.
A look at load balancing for Exchange Server 2010 using the Kemp LoadMaster VLM-100 virtual appliance.
Microsoft and HP have announced the availability of the HP E5000 Messaging System for Microsoft Exchange Server 2010, a high availability Exchange system in a single appliance.
I recently pointed out the difference between Microsoft and VMware guidance on mixing Exchange Server 2010 DAGs with hypervisor HA features. In short, Microsoft clearly states that hypervisor HA features should be disabled for DAG members, while VMware considers it to be an effective solution