If you look back at the OpenStreetMap diary entries, the vast majority of them make reference to a place the poster has been mapping, but there was no way of actually specifying the location of that place. Now, if you're writing an entry in your OpenStreetMap diary (as any OSM user can) you can also specify a location for that entry.
When people view the diary entry they can now click through to view or edit that area of the map to see what you're writing about. Each pair of coordinates is wrapped in the geo microformat too, so if your browser knows how to handle them, it should be able to pick them out.
The feed of diary entries also includes the location information (currently only W3C geo, but should soon have actual GeoRSS too), allowing you to visualise them on Google Maps, for example, or any other geo-enabled feed reader.