I definitely know about the OpenStreetMap project (and, as a side note, I'm looking forward to meeting some of their developers at Wikimania next week), but I think that application is better suited for Semantic Layers, which is the extension based on OpenLayers. Matt Williamson, the developer of Semantic Layers, has said he's interested in adding OpenStreetMap information to SL (I believe it can just be implemented as a separate layer), but I don't know what the status of that is.
Yaron Koren wrote:[...]
After almost a year of inactivity for the project, I've taken over the Semantic Google Maps extension.
Great that it's actively maintained again! :)
I encourage everyone who already uses this extension to upgrade to the latest version, and everyone else to take a look at it.
Can I encourage you to think about adding support also for OpenStreetMap? They're a great project, very active community and with similar goals (open data) to SMW...