Thanks for the quick reply!
I'm at the point where I have to decide on the backup strategy as well (without knowing all the implication)
The SAN storage array will replicate the data to the DR site.
The local backup media is fast disk (a couple of Dell servers with MD1000s attached)
Currently connected to the 10GB LAN. I can also connect them to the SAN network if there is a benefit.
Besides file level data, there are also smaller VMs with complex software configurations and some physical servers (which need image level backup). Exchange and MS SQL will come into the picture eventually.
I was looking into the performance monitoring aspect of ESX and that gets complicated fast too! Would you have some links for a good starting point?