Old thread, but nonetheless, I'll throw my view on this motherboard:
The reason why it's expensive is because it's loaded with stuff you won't see on most if any similar motherboards (true for most Supermicro motherboards). The board has a real southbridge, ICH9R, which can do RAID 0, 1, 5 and 10 and offers 6 SATA 3Gb/s ports, not 2 like NM10 (which doesn't do RAID either; I believe you need Windows for RAID 5 on Intel southbridges anyway). In addition to that it has two
Intel 82574L Gigabit controllers - most boards have one, maybe two but Realtek, which in my experience (and many who have used both) Intel makes some of the best (speed and reliability) ethernet controllers. You also get PCI-E 2.0 x4 in an x16 slot for expansion, as well as one USB 2.0 port intended to for a flash drive to boot from; there's also a 4-pin molex to power fans or other low-power stuff and two 4-pin PWM fan headers.
The most important thing about it is it's integrated video chip (Matrox G200eW is nothing spectacular, VGA output and 8MB DDR - that's the amount of cache
quad-core CPUs have) and IPMI with a dedicated Etherner port. This is for a really awesome feature this board is all about - remote management, you know, the thing you get with Dell's iDRAC cards. I won't get into detail about that, as Patrick @ ServeTheHome has written a lot about it
(and about Supermicro in general), so just head there and read his post - it's extremely detailed.
This board is easily worth it's price, just like most Supermicro boards (on some boards the onboard components are worth more than a motherboard + those purchased separately, like X8ST3-F or X8SI6-F).