There's a difference between having blurry photos and purposely using blur. The easiest way to tell is if the things you don't intend to blur are tack sharp. For example, in the photo above, the flag above and the man in the bottom right corner are not blurry, whereas the moving people are indeed blurs. When the entire photo is blurry, it's due to camera shake and just screams "mistake" (click here to find out how to get sharp photos). To achieve this effect, use a low shutter speed (here: 1/4th of a second) and use a tripod (or hold really still, like I did).