Maybe I overlook? Are there turn-by-turn navigation api yet? Over the last year, every time I check it seems to be not available yet. I believe most or all streets in OSM only support up to street level rather than street NUMBER level. Well, please point me to some counter-examples if I am wrong.
Try out OSRM[1]. It is open source[2], so you can run it yourself, or you can use a public api for limited usage. The api has a JSON response with turn-by-turn[3], and it is remarkably fast.
Wow, speed is great. I'll definitely check it out. However, the second statement still seems to be valid: OSM is still at the street name level rather than street number level.
I read some MapQuest's document saying that Mapquest actually took points on a street and interpolate all the numbers. Maybe OSM can do the same. Eagerly waiting...
OSM does have addresses, but coverage is far from perfect. Nominatum (the geocoder used by OSRM) will interpolate addresses if it does not have the exact parcel info, which is surprisingly accurate in many cases. Work is also being done to create full address coverage as well[1], which you should check out if you are interested.
Routing is coming to osm.org real soon now, and as morganherlocker has pointed out, the software is already widely available (and used) elsewhere. But yes, house number data in OSM is partial at best.
