The I2C ports are not enabled on the Raspberry Pi/Raspbian by default. Not too hard to get them working though (instructions derived from the Adafruit post here).
Details after the jump…
Add the following two lines to /etc/modules:
Then comment out the following line in /etc/modprobe.d/raspi-blacklist.conf:
# blacklist i2c-bcm2708
Restart the Raspberry Pi and /dev/i2c-0 and /dev/i2c-1 should appear. It’s also useful to install the I2C tools:
sudo apt-get install i2c-tools
sudo i2cdetect -y 1
will detect any devices on /dev/i2c-1.