ECC can be pretty important for long term file storage as well, especially if you are using software based raid such as ZFS. I ran my NAS for three years without ECC but definitely decided for it when I upgraded the hardware earlier this year.
See an example here:
http://forums.freenas.org/index.php?threads/ecc-vs-non-ecc-ram-and-zfs.15449/
Understand that, I am using software RAID 0 with non-ECC RAM as well. The risk of the non-ECC RAM cause you trouble most likely is much less than that cause by the HDD. Everything is possible, even though ECC RAM can give you undetected error if 2 bit fail at the same time. It's just a matter of risk management. In this case, we should handle the threat from HDD, but not RAM.
Of course, if money is not an issue, using ECC RAM is 99% better (except it may run 1-2% slower than non-ECC RAM). However, my strategy to handle this risk is by having proper backup x2, rather than using ECC RAM.
Since the chance of having trouble from non-ECC RAM is so small, and I am not running a commercial mission critical server (e.g. Google). Therefore, I can afford a non-ECC error, and spend (up to) few hours to recover the whole system or any files. In reality, I spend few hours per season to upgrade my OS, but never have to recover it due to non-ECC error. Therefore, the potential time cost simply not an issue here.
IMO, once have proper backup, ECC is not important any more. In fact, for any file storage system, backup is much much more important than ECC RAM. ECC can keep the system alive, and able to detect error before system break down. However, it cannot replace proper backup. And for a normal home user, backup should be very important, but not ECC.
I am not saying that ECC RAM is useless, or bad. In fact, I love ECC RAM, and it may be very useful when something goes wrong. However, it's just not that important in a storage system, or a home use file server.