The more you play with OpenStreetMap, the more magical ways you start discovering that you can use the data. Two that I've recently found...
1. Water fountains. Here in London, we used to have lots of water fountains. Then modern capitalism found a much better way of delivering water to people: put it in plastic bottles, drive it half way around the country (or world) and sell it to people and a massive profit, who then drink it and throw the plastic bottle away. There are a few water fountains in London though, and they are listed on OpenStreetMap. Any movement to campaign for change requires actual data to start with.
2. Stopped clocks. There are hundreds of beautiful, historical clocks on public buildings across the country. It's possible to mark clocks on OSM, and I've just been discussing on the wiki how we can mark disused clocks. Having the data lets us campaign to have these clocks restarted.
I'm also finding that in the process of doing OpenStreetMapping, I take a lot of photos which are also usable on Commons. Quite a lot of them aren't (for copyright reasons or scope reasons or just because they are pretty crappy photographs), but a lot of the time you can find uses for them on Commons. (Just need to go through and write descriptions, categorise and upload.)
I heartily recommend any Wikimedians grab themselves the relevant tools for OSMing (which don't necessarily mean a standalone GPS device: things like iPhones and Android smartphones can be used, and you can even go low-tech and print out walking maps), go out and do it. If there's an OSM community in your area, go hang out with them.
The systemic bias issues that Wikipedia face also exist on OSM: here in London, the city is richly documented and the OSMers are mostly just tweaking, fixing and maintaining (most of my edits in London are just metadata improvement rather than actually adding any new shape information). But if you go and look at many non-Western countries, you'll find whole towns which just aren't covered at all.