I am experienced with GIS, but new to QGIS and open source data.
I recently opened an OpenStreetMap (osm) file in QGIS 1.8 (on Kubuntu 12.04). I found that when I selected a feature, there was no colour change to highlight it. I know it was selected because a "zoom to" took me straight back there.
When converted to a shapefile the selection feature highlighted as I would expect.
Is this a bug in handling osm files, or is it something to do with the structure of osm that I haven't understood?