I have about the same setup, but i built my server from scratch have 62TB and I run FreeBSD 9 (plus SSD for os). OS reliability wise and ZFS maturity FreeBSD > Ubuntu. You'll have virtualisation through virtualbox if you'd like to too. But I prefer to separate the storage and virtualisation platforms (do one thing etc). In some ways BSD is easier and more logical in it's setup and administration, plus you'll have better documentation on the site and higher signal-to-noise ratio in the forums, if you need help.

Despite being a heavy computer user I'm positively struggling to fill 1TB even after 2 years of hoarding HD rips, so I'd love to know what you use 62TB for. Also wondering about idle power consumption.

bah, formatting error. 6 times 2TB not 62TB. Everything runs of an atom card, with modded cooling for the bridge and cpu (fan less, really awesome, copper heat sinks). The discs are the WD Caviar Green, low power, and they are attached with rubber to silence them. There are two (90 cm) slow spinning fans in front of the disks, one in the quitet zalman psu (120 cm) and one (90 cm) at the back. I built it in an htpc chassis.