There's tools to convert the OSM data to .img (the file format used by Garmin GPS units and Mapsource) but it's complicated and not within the realms of most users.
Fortunately for us, there's a guy who's hosting the .img files on his website (because the data is under a free license, he can do that
) for all the Australian states and he updates them weekly. Goes by the name of Stevez. I haven't yet loaded them onto a GPS as only my girlfriend's has mapping (Sendmap is the software here I think) but I was able to use a program called M3 to load the .img files into mapsource (I hear there are lots of different programs to do this.) Had to rename the .img files though (details on gpsaustralia forums.)
For anyone else who wants to load the .img files into mapsource and doesn't yet have an application for it, M3 unfortunately requires you to register for an account on the maker's forums before you're able to download it - this is free and requires only a couple of minutes and a valid email address, but it's a bit of a pain. The forum thread is here. If anyone can recommend a similar, easy to use, free product, I'd be happy to try it out.
So as you'll see when you get a look, there is most likely data missing from your local area. Perhaps you're like me and the first time you look at it, your city only has some major roads filled in. Perhaps you live somewhere rural and there's nothing at all. Or perhaps you notice that your whole neighbourhood is marked, but your street is misspelled. No matter how much or little data there is around your place, you can contribute to OSM to improve it.
There's a few ways to get involved, but one that's especially easy for Geocachers is to upload their GPS traces.
Get your gps to trace your route when you go out caching and then upload it to the website. If you really want to contribute, you can then draw "ways" over it (a way is a specific path, for instance a highway or a cycle path or a walking track.) You can then tag the ways so they show up on the actual map. Tags identify what sort of track you were travelling on, and there are tags for loads of different things, with more being added all the time. highway=primary, highway=residential, waterway=river, railway=rail, railway=tram, are some of the more common ones, but there are dozens more.
If, however, you don't want to do that, just uploading your track and making it publicly viewable is a great contribution - someone else can come along later (perhaps someone without a GPS, but who knows the area) and create and tag the ways.
There's lots of other stuff that needs doing too, read the Get Involved page I linked above.
Unfortunately their wiki isn't the best (eg. quite a bit of old information, needs tidying/refining in places) and it's quite a steep learning curve to start mapping, but they have an IRC channel which generally has helpful people hanging around, or you can ask me and I'll try to find an answer for you (I've only been interested in OSM for about a week though...)
So yeah, that's my rather long introduction... if you have any queries, I'd be happy to (attempt to) answer them.
Note: Not sure if this belongs here or in General Chit-Chat (as I'm new here.) If a moderator could please move it if it's in the wrong place, that would be appreciated.
