I'm using Clozure Common Lisp on my Raspberry Pi to control living room lighting.
That is 10m of individually adressable LED strip (this one http://www.adafruit.com/products/306
via the Raspberry's SPI port, a GPIO pin as main switch and an USB microphone for
capturing speech commands (and for spectrum analysis to control light effects)
The Lisp process is started when booting and starts Hunchentoot web server
to be controlled by a mobile phone browser via WLAN and a swank server for
remote development/debugging from an Ubuntu laptop, so no keyboard/mouse
or display is connected to the Raspberry and I access the Raspberry by ssh.
By using the WiringPi library http://wiringpi.com/
the IO pins can be accessed
as files, e.g. /dev/spidev0.0 to output data to the LED strip via SPI, or
/sys/class/gpio/gpio17/value to read the GPIO pin 17. This library also
allows running your Lisp process as a non-root user.
The project is still in progress, so I can't publish the entire code yet, but once it's
finished, I'll do so. Stay tuned...