I'm working on a patch/plugin adding support for creating parallel ways to JOSM.

The current form is a patch to the core, but depending on how people feel about including it in there and how fast the quality improves, I might change to a plugin.

Feedback and testing is welcome. (preferably in the trac ticket)

Trac ticket
Pre-built jar (I changed the setting directory to '.josm-dev' so it wont screw up your settings. Only tested on my system(linux) though)

Use Shift-P or the button (same icon as in potlach2) to activate the mode. You may ctrl/shift select ways as in select mode. To create a parallel path just drag one of the selected ways. (or just a single way).

See usage description in the statusline for more.

Probably best to not use it for uploads yet. I'm not that familiar with the code-base and strange bugs might lurk around.

(Edit: added short usage description)

UPDATE: now a plugin: http://wiki.openstreetmap.org/wiki/JOSM/Plugins/ParallelWay

Just found this neat tool: http://www.mappage.org/error/ It makes a gpx waypoint file with selected OSM errors in a specified area.