Filter content by user's location

Hi All,

I'm currently implementing a social networking site using Drupal (5.7)
I intend to display different types of content (including classifieds, events, audio/video samples, user profiles) to registered users depending on their location.

I installed the location.module module and try to figure out how to filter the content exposed to the user based on the user's location.
At the creation stage, each content has a location Field (country + city) wich should be preselected depending on user's registrered location (ISSUE 1)

The idea is then to pre-select the information displayed, and offer to switch from the selected location to another. (like in kijiji.com or craigslist.com marketplaces)

Using a location taxonomy and views I could expose a filter on the content pages and have the user select manually the appropriate location, but How could such a filter be applied simultaneously to a all the content displayed? (ISSUE 2).

I thought about having a different content DB for each location (multisite), but this is getting a bit too heavy.

Thank you very much for you help on this maze great location module :-)
Cheers

loic