It's a wide open question, first thing to ask is when you say most companies, if they use two separate VLAN for Prod & Backup, still they use two separate NIC for separating the traffic.

Thanks

Deb

Deb, I'm not sure what you're saying here. If you're using separate VLANs you don't have to use separate NICs. A network team (e.g. in Windows Server 2012) can easily accommodate more than one VLAN on the same physical connection(s), assuming the switches are set up accordingly. You only need separate NICs if you have physically separate networks (i.e. a separate set of cables).

I also don't see how it's a "wide open" question. I'm simply asking whether or not one is using physically separate backup/production networks. Or, to put it another way, do you use a physically separate network for your backup data?

I don't separate physical networks.  I do have to use different VLANs but everything resides on the same physical gear.  I know some shops like to have dedicated backup networks, for me it's another security nightmare to managed and more hardware to troubleshoot.  All my servers are Cisco UCS with 10G interfaces so it's has not been an issue.

FMonteiro and Dynamox, may I ask which industry sector you're working in? FMonteiro, why would you recommend separate networks in this day and age?

We use both, but nowadays I would say more or less all separation is done logically at VLAN level.  Depending on VLAN, certain network filters/characteristics are made (eg. for what is used for backup we use wide nonrouted VLAN without any port restrictions between backup infra and clients).