With a price tag of around $300 US, the Intel DX79SI isn't a cheap board with cheaper X79 offerings coming in from as low as $219.99 US. There's nothing wrong with the DX79SI, but there's nothing that really makes it stand out that much, especially when you compare it to companies like ASUS, GIGABYTE, MSI and ASRock who offer us a really wide range of boards at different price points.
SATA ports are minimal due to the lack of an extra controller being present; the I/O side of things is just quite bare, period. To run SLI or CrossFire you need to run the cards in the first two PCIe x16 slots for them to run at x16 / x16. With a third slot on offer, though, it feels so pointless running two dual slots cards sandwiched together. The other option is to move it to the end, but then you're moving it to an x8 wired slot.
The BIOS is fine in the sense that we've got a lot of options on offer and it's fairly easy to navigate, but it's got nothing on companies who have really been fine tuning the UEFI BIOS over the past 12 months.
On the plus side of things, the dual Intel Gigabit networking is nice; the color scheme of the board is also good. The bundle isn't too bad with the Bluetooth / WiFi module included, albeit not in ours today. The 3 Year warranty on the board is also really nice.
The issue is that these aren't really enough for us to go, "I'd pick this over an equivalent option from someone else". At this price point you can pick up the MSI X79A-GD65 or ASUS P9X79. An extra $30 US, though, will get you the PRO variant of the ASUS board or even a GIGABYTE X79A-UD5.
The Intel DX79SI isn't a bad motherboard, but amongst the cut throat industry that is motherboards, it doesn't stand out against boards from the companies we've already mentioned. Unless you needed to have an Intel board, we'd probably suggest you look at some of the other feature packed offerings from companies like ASUS, GIGABYTE, MSI and ASRock.
The final issue is that the board just seems hard to find - it's not listed at Newegg, Frys or Tiger Direct. With so many other options available to these companies, it's probably not a huge surprise, though.