For all those using Load balancing with VMware, you will need to configure a NLB portgroup to avoid port flooding. To prevent RARP packets being sent every time vMotion or powering on a VM, you will need to configure no notify switch on the required portgroups. If you are using unicast, you will also need to set the Security Policy Forged Transmit to Accept.
Ryan Mangan's IT Blog 
One question, When you say NLB you are refering to Microsoft NLB? We are experiences some issues with Microsoft NLB flooding all the ports on the switch but we haven’t change any setting on the VMware virtual switch.
Thanks
This applies to MS NLB and Application delivery Controllers (load balancers)