Each of my four bikes that were stolen were stolen while "parked" on the street and chained up. The bike thieves find crafty ways too break locks. My bikes have been stolen in the evening time, but I have had friends get theirs stolen in broad daylight, too. I have heard that people may try to jack your bike while you're riding it, but I haven't known anybody that's happened to. The most is a threat of getting something yoinked from your basket, but for the most part I think if you keep moving, and keep whatever is in tow "tied" down, it'll be ok.
The last bike I had stolen was locked up to the fence of the Konex (a music/events venue in Abasto--a bit of a dodgy neighborhood, but not the worst either). The poles were big thick steel poles, there is a ton of outdoor lighting, people, and even security guards there. The thieves actually broke the POLE that my bike was attached to, then slipped the bike off from where the pole was broken at the weld seam. I found the u-lock twisted and broken open a bit down the street. It was a pretty dang nice bike that I loved, too (A vairo metro), so I was crushed. The security guard just snickered, so maybe he was in on it. Hijo de puta.
Anyway, now, if possible, I bring my bike inside with me if I'm going somewhere at night. Even if that means carrying it up four flights of stairs. Even after all the thefts, I continue to ride (and buy, ha) bike here.
