Without looking at the auction i can say this about miniITX.
1. They generally don't have many HDD (whether that be SATA or PATA) ports. 2. If they have expansion slots then you'll be lucky to have one of them PCI 3. Following from points 1. and 2. above, if you get a miniITX board that comes in a case you can't really fit many HDD's in there so becomes a bit redundant for a file server. And if you have one with a PCI slot on it then you'll likely have to fit a low profile card to get it into the case. This can be a pain if the card you want doesn't fit i.e. a specific TV card 4. The integrated graphics chip is poor. This will likely change in the future.
They all become redundant if you're just buying a motherboard to fit into a standard ATX case you have lying around.
Have a look at some of the VIA options. They have integrated CPU's. This is great for heat e.t.c. as you can run most of them passively (without a noisy fan) but they don't have enough grunt to deal with h.264 videos or TV streams.
I'd probably use a VIA miniITX board for my file server in the future maybe one of their new NAS 7800 boards. It has a bunch of SATA ports and a fairly beefy CPU. Graphics don't matter on a file server.