I note a change in the local street culture while strolling in my sister's Chicago neighborhood (West Rogers Park, which for auslanders means "far North Side"): lots more people riding bikes on the sidewalk around here. Impressions are undependable as data points, but I'd say that I might encounter an adult riding down the sidewalk maybe once a day on prior visits here (if that). On this visit, I've encountered multiple cyclists, sometimes flurries of them, every time I've been out walking. These don't appear to be really serious, gung ho cyclists--we saw a group of them whipping down Western Avenue, in the street with full lights, etc., at dusk last night. No, these look like folks, like the guy above, who are out on short errands and have figured out that rolling is faster than walking and perhaps less complicated than driving. Sort of a good news (great to see more people on two wheels), bad news (bikes and sidewalks don't mix well, and it's illegal for anyone over 12 years old to ride on the sidewalk in Chicago) story. The illegal riding is complicated by the lack of etiquette and riding smarts on the park of most sidewalk cyclists: They rarely make a sound when they're coming up behind you (Kate nearly got clipped by a teenager just on Sheridan Road just up from Loyola Park.
In any case, the issue is not a new one here. When my folks lived at Sheridan and Ardmore, there was an ongoing issue (and still ongoing) with cyclists emerging from the north end of the lake shore bike path and deciding to continue their journey on the sidewalk rather than on a parallel bike route a short block to the west. (Bike lanes of course pose their own set of challenges, including drivers who whip their doors open into the two-wheeled traffic zone.) The city has installed threatening signs and painted the message on the sidewalks there--by city ordinance, you'll get fined and have your bike temporarily disabled (what do they do? take one of your wheels?). Last time I walked there, sidewalk cycling was still common.
The city government's Chicago Bicycle Program has a decent instructional video on the issue: Bike on the Street, Not on the Sidewalk, which actually features some staged but still audacious examples of folks dealing with automobile traffic on the streets.