I think the title says it all. I know it doesn't have terribly much to do with HTPC (man do we need a better name for this section!) but I'm looking at a Mac Pro and wondering what advantage having 2 GigE ethernet ports would offer? My GigE switch isn't really a bottle neck, so I can't see how having a direct connection between two devices would be preferential, I'm sure I'm missing something obvious, do tell :)

A second NIC is very handy in some common Mac Pro deployments, like as an Xsan client. The Mac Pro is really designed as a workstation-class computer, and a second NIC could be used for all kinds of things. Generally speaking, you wouldn't have much use for it at home, but hey, it's there. :)

Thanks! A couple minutes reading about Xsan helps me get the general idea. Can anyone else elaborate on some of the 'all kinds of things'? I'm not doubting madSkeelz, I'd just like to know what some of those things might be.

Well, just to give some other ideas...

Link Aggregation is used every now and then for redundancy or throughput:
http://en.wikipedia.org/wiki/IEEE_802.3ad

Generally speaking, you see that sort of thing on a server, rather than a workstation though.

Some people like to use one NIC for general ethernet usage and the other NIC for iSCSI-only traffic.

In more complex environments, you might have the NICs connected to different LANs, so that a machine can access resources on both networks, without having to combine the networks themselves. [Maybe you have a public LAN and a secure LAN, and need a machine to straddle both.]

I really can't think of a good use for both NICs in a home network though. Maybe someone else will have ideas.