Do you like running? The Nike+Ipod Sports Kit fits perfectly to your needs.
When I bought this gadget some weeks ago I was a bit averse. I didn't believe that this cheap sensor (30€/$) could measure my training accurately. I was wrong.
Like in all company products, Apple have achieved again a perfect symbiosis between simplicity and power. For people who like go running this is a perfect gadget. Apart from the functions of a normal music player, it has some extra ones that make the difference. You can measure your distance or your pace, you have the information of pasts trainings stored and maybe the most important, you can inject some extra forces with the PowerSong. The PowerSong is only a song that you preset before go running and it's the song that makes you run faster or give you extra motivation. Apart from the functions of the kit, there is a good community of runners. On Nike website of Nike+ you can interact with the community and you can view your history. There are other interesting features like set goals and see if you can achieve them or challenge other runners to see who is the best.
To get this features up and running, you hace to tune your kit. The tune process consist on plug in the receiver in the Ipod and put the sensor in your Nike+ Shoes hole. For those who can't pay for a new shoes, like me, there are some solutions like buy an adapter o make a homebrew hole inside your shoes reed.
For ending I have to say that the sensor doesn't have the possibility of changing this battery but Apple people says that the sensor's battery should outlast five pairs of running shoes. Would it be true?