I have done bulk imports to OSM before for UD/Newark Data. I used shp2osm (http://wiki.openstreetmap.
Here is a comprehensive page on doing bulk imports: http://wiki.openstreetmap.org/
OSM gives priority to smaller edits, as part of its grassroots philosophy. Partially because of this, it's important to tread lightly when doing bulk updates. That's why I like JOSM. I can see the existing data and how my updates will change that (if so) or potentially create duplicates. The imports guidelines link (http://wiki.openstreetmap.