Having lived in a variety of cities from the quite large to the small farm towns, it never ceases to amaze me that so many people are comfortable leaving their bicycle unattended and unlocked. Even though I grew up in a somewhat small town, I think I've always had "city mentality," meaning that I don't leave anything unlocked (to this day, it drives family insane because they don't understand where my thought process comes from). Currently, we live in a fairly safe city where very little crime beyond tagging and the occasional theft take place, but I still hold firmly to the idea that doors should be locked at night, bikes should be put away, strangers shouldn't walk behind me suspiciously close at night, and anything I'd like to continue to hold in my possession should be out of sight of any passer-by.
I will admit that when I'm doing quick drops at the post office, I have, on occasion left my bike unlocked, but I can also see it through the window and I'm inside for less than 20 seconds. What do you think? Do you lock up your bicycle everywhere you go, or are there locations where you feel safe leaving your bike unlocked?