Nike SB actually stands for Skateboarding, which they focused this line of product for skateboarders. There are lotsa varieties in the SB line ranging from clothing to shoes. As for today i could see most ppl used them for casual use too, and theres a number of celebs worn them as seen on many events. So i think in sense of fashion, there is nothing wrong to wear your SB's as long you feel comfortable and suitable with your appearance. You can read some info's about SB here.