One of the nice things about the Raspberry Pi is the that it doesn't require a lot of power to run. This means you can leave it on all day long without it putting a dent in your electricity bill. To take advantage of that, How-To Geek has a guide for using your Raspberry Pi as an always-on Usenet machine.
The setup hinges on SABnzbd. It includes setting it up to start automatically, UNRAR files as they come in, and sending all the files over to an external hard drive. The nice thing is that you can tap into SABnzbd with a mobile app so that you don't ever really need to look at your Raspberry Pi.
If you're a big Usenet user who consumes a lot of power with a desktop PC that's always on and downloading, this low-powered solution is certainly worth a look. Head over to How-To Geek for the full guide.