I am not a VMWare expert and my main knowledge is in networking but I've used ESXi 5.1 update 1 enough. We have a ESXi 5.1 update 1 environment that has been having issue for almost six months now. We opened a TAC case with VMWare for about six months now without any resolution insight.
We are running ESXi 5.1 update 1 on Dell Server poweredge 2950 with the latest firmware. We have redhat linux 5.8 64 bits guest OS on VMware. We have a multicast application running on the redhat linux guest OS.
We are experiencing multicast packet loss. After careful analysis from the network side, we've concluded that the multicast traffics actually gets to the physical interface of the ESX host but it is not being forwarded by the VMware distributed virtual switch. For the past six months, we spend countless hours and resources working with VM TAC support to resolve this issue and it is going anywhere. VM TAC confirms that the packet is not being forwarded by the virtual switch but has no resolution for it. A lot financial applications utilize multicast.
VMWare is definitely not ready prime time and especially for mission critical applications, as described above.
my 2c.