1) Create a launcher (either on the desktop or in a folder) with, say, the
"Create launcher" item from the contextual/right-click menu.
2) Have the launcher do something simple, e.g., "http://www.gnome.org".
3) Attempt to edit the launcher through the "Properties" item on the contextual
menu.
4) You can edit metadata for the launcher, but not the command the launcher
runs.  I expect to be able to edit the original fields I specified when creating
the launcher, so I can change the URL, generic name, comment, etc. 
5) The Properties menu is only wired up correctly when the launcher lives in a
panel, so there is a clunky workaround of copying the icon to the panel, editing
it there, then moving it back to the desktop or original folder.