We use SAN Replication for our DR. It isn't quite real time, but it isn't far behind it unless there is a lot of disk movement happening on the SAN at which point it will queue up until it either tips over and replication splits, paging our SAN Admin, or the activity slows so that the replication catches up.

Without a full picture of the Host, # VM's, types of VM's # spindles assigned to the LUN it is impossible to actually tell what was most problemattic for your particular example. Having a shared LUN is certainly somewhere up there in the list near the top. I got a email from someone last year asking how I could recommend SQL on VMware after they attended a session where I discussed this topic. They had 4 SQL Servers on a single host and were having huge performance problems. Turned out that they were using DAS in a RAID 5 with 4 300GB disks. There is no way in the world that you will get good performance with that configuration. I personally would have issues running that configuration for a single production SQL Server physically, let alone 4 of them virtualized on that hardware.

The up front cost to building a Virtual Infrastructure that is going to provide good performance can be very steep initally especially if you don't have a SAN, and if you are going from a bunch of small 1 or 2 way servers to a 4 or 8 way host type machine. Sure Virtualization is touted as a way to make better use of your existing hardware, but you need to take a serious look at what your existing hardware actually is, and then size that up with your actual expectations.