How do you know if your Twitter is getting a good workout? By charting its progress with a Nike+ FuelBand, of course. That's the thinking behind Stinkdigital's Tweetfuel, which reacts every time there is activity on its Twitter account. Whenever somebody retweets, follows or mentions the brand, its customized motorized kit spins the band. Accumulated 'points' can be used as a metric of its activity on Twitter.