The Canadian Internet Policy & Public Interest Clinic (CIPPIC) has an interesting piece on the legal risks of contributing to and using Volunteered Geographic Information … in other words, OSM: Volunteered Geographic Information FAQ.
The document makes a few observations (from a Canadian legal perspective) that mappers might find useful. In summary:
As a mapper, you're unlikely to be sued if you add incorrect data to OSM. But you wouldn't (knowingly) do that, would you?
OSM (or OSMF, most likely) would unlikely be liable if map data were relied upon in an emergency and found to be incorrect. There are many nuances to this, so it's better if you read the When would a VGI website be liable in negligence for inaccurate information? section yourself.
In order to limit its liability, OSM should “… also make sure that their software is running smoothly, and that the visual designs of the sites are clear and informative.” Hmm.
(Incidentally, CIPPIC is also responsible for the excellent-though-depressing CIPPIC Licensing Information Project for Open Licences, CLIPol. If you want to see how not to do open data, take a look at some of the really bad licences they've found. I wonder why so many of the terrible “open” government licences are near me?)