I was in Chicago a couple of years ago, and will be going back this summer. When I was there, I was struck by a couple of things:
Aside from the south side of the city, Chicago is, hands down the cleanest big city I have ever visited. Trash was nonexistent. Little patches of grasses and flowers are planted all over the place, making the whole area feel cleaner.
I was stunned at the overall friendliness of poeple there. On the bus, people routinely gave up their seats for the elderly and disabled without anyone asking them to do so. Certainly, the city has an enormous population, but the vast majority were quite friendly.
I walked the theatre district at night, down to the Navy Pier, and never saw any reason not to do so. The city is well lit and well patrolled.
Use your common sense, but I think that Tann's estimations of horrible ganbangers may be a tad overstated.