I used MediaTomb and NZBGet with some post process scripts - working together it's the perfect media download / serving box.
Would download NZBs from my (android) phone, upload the the NZB to the boxes FTP server in NZBgets NZB directory, and then wait for NZbget to download - once download the postprocess script would par (if needed) and unrar.
Watched media on the PS3 mainly.
Mediatomb would scan for new files every hour or so.
Obviously this is when it (external USB hdd) works!! (see my other thread!)