I've had the Chicago city notebook for a couple years now and I never go to Chicago without it. Part of the reason is that I have collected a fair bit of information about locations of stores and restaurants I've enjoyed, and part of it because I have found it to be so useful. The maps cover the entire lake shore region, from south of the University of Chicago north past Lincoln Park Zoo. The detail in the main 'downtown' area (the loop and Michigan avenue area) is more than enough to make navigating the streets on foot or in a car quite easy.
One anecdote for why I love the Moleskine so much: I was in Chicago a little more than a year ago and was walking between our hotel (Merchandise Mart Holiday Inn) and the Tribune Building area and met a couple of other tourists at a cross walk. They were looking forlornly at their smartphones for a train depot. They asked if I was familiar with the area and where the nearest station was. I pulled out my analog device (the Moleskine!) and showed them the location of their station! Paper: 1, internet: 0.
I wish that the City Notebooks (and in particular, the Chicago one that this review is about) had two additional things though:
1. More map coverage. Coming in from Lake Michigan quickly runs one off the map. I don't need all the way to O'Hare, but another page or so in in some places would be nice. Especially in the Milwaukee Ave. and west Fullerton areas. These are gentrifying quickly and there are really nice restaurants out there that the map doesn't let you chart your way to.
2. Stickers to mark important places on the map. Certainly there are the pages to write in and the tracing paper to chart a route, but nothing is quite a quick as putting a sticker on the map at an intersection so that when you open to that page again you know exactly where the place you're looking for is. I would have appreciated marking my hotel, or particularly good restaurants, or even marking the location of a place I never wanted to forget (and was significant enough to stick on the map). I probably wouldn't use them all the time, but I definitely would use small stickers on the maps.
These notebooks are well-built, easy to use, and I don't travel without checking to see if the city I'm going to has one. In those cases I buy one!