What are the minimal system requirements to run a full Bitcoin node? I want to build a low profile system running as a full Bitcoin node, i.e. just running Bitcoin Core 0.9+ and pretty much nothing else. What is the minimal system (in terms of power consumption) that would be suitable for this task? Just bitcoind will do, no interface or visual interaction needed. 

I'd really prefer something where I don't need to build all the software manually.

A simple small netbook would do, I guess. But could I even use something like a Raspberry Pi? Or perhaps some other single board computer?

I assume it'll need at least 20-30 GB disk space (for OS + Bitcoin Core with entire blockchain). Is there a minimum amount of RAM I'd need for bitcoind?

Curious to hear what kind of system and OS you guys would recommend for this!

(P.S. to avoid confusion: I just mean running a full Bitcoin node, not mining)
Just some thoughts:


As of the time of writing the main net's full blockchain size is 21,670,092,800 bytes, a bit more than 20 GB, that is. So you should have way more disk space that just 20-30 GB.
A Raspberry Pi runs with an SD. SD is known for its limited rewriting capabilities (it's not a heavy duty storage solution, it will bite the dust after a while) and on top of that there's also the very important factor of the data transfer rate. SD's top model type (Class U3) maxs at 30 MB/s while a typical SATA-3 disk will max at 750 MB/s, which BTW can go as high as 2 GB/s with a SATA Express attached to a twin PCI Express 3.2 lane, but I guess this is not a low-spec computer any more. And yes, I know, you can mount an external USB HD to a R-Pi but even in this case you'll never get these speeds.
Some of the top single board computers could perform well, and I think this is the best solution for a low power-consumption full node. For example if you attach a SATA hard drive to IGEPv5 Full Version you will most probably get quite good performance at a very low cost, both of acquisition but operational as well.
A low-spec computer could deliver great results with some lightweight linux distributions, my personal favorite is Lubuntu that comes with an LX11DE UI and then bitcoin's installation would be as easy as: 

Menu &gt; Accessories &gt; LXTerminal &gt; $


sudo add-apt-repository ppa:bitcoin/bitcoin
sudo apt-get update
sudo apt-get install bitcoind



Edit 1: Pictures speak louder than words (as a response to Jannes's comment, so I'm attaching a few performance screenshots from a full node running in Windows that just received a new block and a couple of minutes after that, as well as an analysis of the I/O index:

Verifying incoming block:



One of the I/O spikes of the block verification at level 3 (default for all clients):



I/O analysis for the above graphs: