Although makers tend to get carried away creating fun items of various levels of usefulness, the Arduino platform can always be used to build items that are genuinely useful and able to improve someone's life. One example of this has been demonstrated by Instructables user "Mizchief100" with their VIP.
It's a fantastic haptic-feedback device that works well and is also quite simple - it's a small box that fits underneath the wrist of the wearer that contains an ultrasonic distance sensor, small vibration motor, a small Arduino and associated circuitry. It allows the distance between objects and the user to be communicated by vibration - perfect for visually-impaired users. Consider the following demonstration:
Very well done, and a fine example of using the Arduino platform. Complete instructions can be found from here. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
To get started with your own embedded-Arduino projects - look no further than the Freetronics LeoStick. Apart from being one of the smallest Arduino-compatibles on the market with USB, it also has an onboard RGB LED and piezo for sound and knock detection: