This time it's Microsoft that's making nice, adding an OpenStreetMap layer to its Bing maps. It's just one of a number of changes to Bing Maps, and the new maps require the latest version of Microsoft's Silverlight.
With Yahoo having worked with OpenStreetMap since 2006, and calling regularly for open location rather than proprietary advantage, OpenStreetMap has even become competitive with Google Maps, especially in places where proprietary data is in short supply, like Tehran.
OpenStreetMap affords Google's competitors an easy way to add technical competitiveness to their offerings, but in exchange for that OpenStreetMap itself becomes more competitive with what Google offers.
It must be added at this point that Google is on friendly terms with OpenStreetMap, having had projects in its Summer of Code for the last three years running. OpenStreetMap tiles as a layer onto Google Maps as well, so who needs the Google Maps API?
This is really what open source is supposed to do, wear down proprietary advantages, providing an interoperability layer among proprietary systems, making things better.
The OpenStreetMap Wiki assigns what it calls the LOLcat of Awesomeness to those who make a big contribution. I hope they don't mind if I copy it here and point it back at the team. You know who you are.