cadastre-fr is a plugin for JOSM that is able to handle the
french land registry WMS. This WMS is not a complete standard WMS
since it is not providing most of the standard services. It is also
just delivering data for one municipality at a time. A special request
is required at the beginning to specify which municipality is desired.

The plugin is today only requesting PNG images on user request only. The
images can be stored in a cache file and reloaded later. The grabed images
can be done at any zoom level and the drawing method will always select the
best images (highest scale) to be displayed in front of worst images
(lowest scale).

Also the plugin is able to transform original images to add the transparency
or replace the default background by the JOSM background color. Enabling
transparency gives the possibility to use several layers, each layer with a
different municipality, making contrbutor's work much easier.

Access to the french land registry WMS has been granted by the autorithies (DFFiP).
It's opened not only for OSM but for all GIS applications. A new version of the
WMS will take place mid 2009.

Announce here (english):
http://lists.openstreetmap.org/pipermail/talk/2009-January/033289.html
First announcement here (french):
http://lists.openstreetmap.org/pipermail/talk-fr/2009-January/005790.html