Kalle Lofgren has distributed a series of RF receivers throughout his house to do some home automation. He has now set-up a Raspberry Pi as an RF control hub. There are extensive instructions on his blog on how to do this with an nRF24L01 RF breakout board. There are other pages on there to do with his set-up. Read more here

As an aside, there’s also a rather neat way of testing out SPI by connecting the MISO and MOSI pins and running a test script.