I'm planning on building a system for DV editing. The motherboard I'll be buying supports ECC memory (Intel d875pbz). Is ECC necessary? How will a memory error manifest itself in a final render? Will it even be noticeable?

Thanks in advance for any input.

Nope, you don't need ECC memory.

ECC memory allows for ridiculous amounts of RAM. 24GB I think?
ECC memory has error checking, but that doesn't help you much. In the extremely rare case you get an error, you'll get a dropout or something like that if rendering a video file. Nothing major.

A memory error can be more serious than that. You can easily crash the entire machine if one bit goes wrong, especially in the instruction stream.

ECC in most forms is only an additional one or two bits of parity,
which is enough only to identify an error. Thus, it's only an error test. You need about 9 bits of parity for 16 bits of data to actually correct it. There are many schemes for this.

Registered memory has error correction.

But really... the chance of a memory error is very, very low (assuming you have good memory in the first place, try memtest86 if you want to test) and it's not catastrophic when you get an error (dropout, and even rarer your computer will crash).

While the chance of a cosmic particle striking a memory cell are small, there are plenty of other enivonmental factors such as heat which dramatically increase the errors.

In reference to the chance of getting memory error. . . the 50/50/90 rule applies.

If there is a 50/50 percent chance that there will be an error, there is a 90 percent chance that it will happen to me.