[the8472]

Sometimes that's a feature. At least with VirtualBox I have made the experience that NAT virtual networking leads to significant slowdown on a linux guest compared to bridging one of the host's ethernet adapters. I suspect that's due to windows' firewall software or similar things happening in the host system. It also means one less hop to debug when it comes to network issues.

I think the question is whether you consider a VM more like another machine in your network that merely happens to run on the same hardware or a part of the host system.

[rrobukef]

From a firewall POV: Can the host system reliably interact mechanically with the VM? I.e., can the host get root in the VM? If so, a firewall only reduces the attack surface by eliminating the obvious.