I found the oXygen XML editor to be a handy program for finding bugs in my capabilities document. I'm only demo-ing oXygen now but might spring for it if it's equally useful with WMS and SLD. Getting my data into uDig was mostly a matter of tweaking the WFS response and schema into a form that GeoTools would accept. Evidentally, members is not a good typename no matter the namespace.
The service root is
and the online resource URL for capabilities, which you may enter in uDig's WFS data source wizard, is
MapServer users will need to adjust to the change in the typename, using the following layer definition:
LAYER NAME "members" TYPE POINT STATUS DEFAULT CONNECTIONTYPE WFS CONNECTION "http://sgillies.net:9001/mapserver/members/features.rpy?" METADATA "wfs_service" "WFS" "wfs_typename" "users" "wfs_version" "1.0.0" END LABELITEM "zco:fullname" PROJECTION "+init=epsg:4326" END END