For each of the wifi hotspots around town, especially in public places with particular cultural cache or communal access, there should be a blog that anyone can post to. The catch is that you should only be able to post to the blog while you are actually in the physical space. So, to give a Portland example, you could only post to the Pioneer Square blog while you were accessing the wifi network that covered Pioneer Square.
The technical details are a little bit over my head, but I bet someone smarter than me could set up a blogging system that would only accept posts from computers connected through the particular IP addresses on those wireless networks (or something). Each blog would then become a kind of record of the physical space. If something interesting happened there people would record it and otherwise, the blog would just become an accumulation of different people’s impressions of the place. We could supplement the entries with web cams of each of the places. As more and more of the cool places around town come online the network of blogs could grow making for a kind of virtual folksonomic map of the city’s culture.