Thank you, Chris. Those systems are out of my price range but they do look nice.
If you want ECC support, the only components in your build that you have to change are the motherboard, CPU, and memory. Everything else can stay the same.
The Supermicro motherboard appears to be roughly the same price as the ASUS P9X79 PRO.
The E5-1620 is the Xeon equivalent of the Core i7-3820 that you decided on. According to staticice.com it will cost you $315.95, or $26 more than the core i7.
Crucial.com will sell you 16GB of DDR3 1600 ECC Registered memory (2 x 8GB) for $192, slightly less than what they charge for the non-ECC memory that you originally chose. The ECC memory is admittedly slightly higher latency, but the difference in system performance will be negligable. You could, however, get 16GB of non-ECC DDR3 1600 with the same latency as the ECC memory for $132, so we'll use that price for comparison.
A 32GB ECC system will therefore cost you an extra $26 for the CPU, and an extra $120 for the memory, a grand total of $146. That seems like a modest price to pay for a significant reduction in the risk of data corruption. (I've used US prices; you'll probably pay more if you live elsewhere. The price difference is higher here in Australia because the Supermicro board is hard to get and expensive.)
It's worth mentioning that a lot of AMD motherboards and most of the AMD processors support ECC. I chose a Phenom II for my last build (in early 2009) for this reason. Unfortunately AMD performance is now so far behind Intel that they are no longer a serious contender.
There are those who say that memory errors are rare enough that they can be ignored, but that view may unfortunately be incorrect: http://www.zdnet.com/blog/storage/dram-error-rates-nightmare-on-dimm-street/638
One final disclaimer - I've never actually used a Supermicro board, so I can't vouch for them. They are designed for enterprise use however, so hopefully they are reliable.