It is REALLY worth it!
I used to run a lot before I moved to the city I currently live in. Then I arrived to chilangolandia and for several reasons I stopped running. I started gaining weight (about 22 kg / 45 lbs in 2 years). In these 2 years I'd tried several times to start running/exercising again, without success. I even bought a treadmill so I could stop blaming the city for not having a place for me to run safely. Nevertheless, I couldn't take again the habit of running as before.
About 7 weeks ago, someone robbed my old iPod mini (and old comrade that went along with me in any run I took), so down I went to sears to replace it (I use my ipod a lot while walking/commuting from home to work at several hospitals). I like my iPod to be small, therefore I don't like neither the classic nor the new touch, so I settled for a nano.
Once there I saw an old nike+ kit with a big discount (it seemed to have been there without selling for a long time, hence the discount). Then I remembered the Nike+ challenges that Ziwi had been posting in the Macrumors fora and felt a sudden impulse to get it. Luckily, there was also a credit promotion that allowed me to spend more than what I was planning to. I decided then for the biggest nano, the Nike+ kit and a really light silicone sleeve+armband from belkin.
Next morning, I woke up early (like a child in christmas morning, eager to play with my new toy) and took a run to start using the kit. For this I taped (Scotch tape to secure it firmly in place) the round sensor to my adidas' laces, calibrated the distance in a metered track, and started running.
The first day it was really difficult for me to run a little less than 4 km. But the feeling of SEEING my progress in the screen of the computer was really new to me, and made me feel the need to run more.
Then came the challenges. My God!, when I started joining different challenges (including the MacRumors challenges) I started feeling the urge to keep running and running, because whenever I felt like I could not run anymore, I remembered about that extra km that I needed to top another runner, and soon I discovered that the "Power song" feature of the kit came really handy on those situations.
Now, after about 6 weeks running (the people that study human habits tell us that we need 21 days [or cycles] to create or destroy an habit) I'm amazed at how the proper motivation (the challenges) and the right tools (my music, the power song, the auditive clues and congratulations that come with the kit) have led me to run even faster and longer than when I was in my best shape but only ran what I "felt" was ok for the day.
By the way, I have already dropped 17 of those 45 extra pounds; and altough I'm still far away from being really "in good shape", I'm healthier than before (cholesterol and blood pressure have returned from borderline to normal) and happy to be running again.
Last week my wife gave me a gift, a pair of Nike+ shoes. So now I have the complete set. Although I agree that you don't need to replace the shoes, you can run with whatever you have.
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EDIT:
This is the silicone case/armband that I got, it's about 5 quids cheaper than the other, altough it looks less "professional"
http://www.amazon.co.uk/Belkin-iPod...7?ie=UTF8&s=electronics&qid=1208650372&sr=1-7
And you can always "tape" the sensor to your laces, avoiding the need to buy the dongle. But I must confess I did that because I didn't knew they sell those things to securely attach the transmitter to your tennis shoes.