This is the importer used to generate the files at http://data.mongly.com.
You can see a demo at http://pots.mongly.com. You can read more at http://openmymind.net/2011/6/20/MongoDB--OpenStreetMap-and-a-Little-Demo
This importer generates more data than what is available to download. It tracks the original node id (nid) or way id (wid) that was used to generate our version of the node. The idea is that these could be used when applying a diff.