Hi there, in my next term I will try to code a general Importer to OSM with a modular structure and easy to use. I have allready ideas but wan’t to know what you think is important, or just to make crazy wishes (good for long time planing) 
Hi,
You might start by investigating ogr2osm
http://svn.openstreetmap.org/applications/utils/import/ogr2osm/ogr2osm.py
By utilising ogr you would get for free support for projections and a bunch of GIS formats
http://gdal.org/ogr/ogr_formats.html
Please consider making an osm2Spatialite exporter at the same, such a utility would be nice to have.
I want to use Java so OGR library will not work.
There are Java bindings if you can tolerate using those http://trac.osgeo.org/gdal/wiki/GdalOgrInJava.
I don’t know if this is a good choice cause I wan’t to have a own representation cause of the plugin architecture. But all right, its an idea 