during the last week i started a small application called pictag to geotag my pictures.
The application is very simple. You select one or more pictures on the list, click on the map and all selected pictures have the exiv tags GPSLongitude, GPSLongitudeRef, GPSLatitude and GPSLatitudeRef set to the selected position. Maybe there are some bugs so make a backup of your pictures before you try it;)
Update: Pictag is now available in Ubuntu’s software-center .