When the NuVinci hub first became available, I had the opportunity to ride one for a week in somewhat extreme conditions, and I wrote the review you will find here:
http://tinyurl.com/2kfdu4 This should answer several of the questions posed in this thread. Also, if you search for "NuVinci" at bikecommuters.com you will find impressions and reviews from their staff, as well. Since my first test ride, I have been using one on my commuting bike, a seriously overequipped XtraCycle. After almost two years of riding this hub on a daily basis, I like it even better than I did at first. For me, the most appealing factors are the absolute reliability of the shifting, the extreme durability of the mechanism, and the continuous ratio. I am a huge Sturmey Archer fan, and I have tremendous respect for SRAM (Sachs) and Shimano IGHs, but for this bike, the NuVinci is the only hub that will withstand the stress that I put on it, and it is also thoroughly enjoyable to ride. It is definitely not the perfect hub for every bike or every rider, but it definitely has its place.