We switched from Google Maps to OSM because they were too expensive. Now that we are using the Leaflet JS lib, we are really happy with it. Not only is it a fairly nice API, but it is open source, so it is much easier to debug than working with Google's obfuscated code. Even with this price reduction, I see no reason to even consider switching back.

The only downside to OSM is that we needed the tiles served up through https since our site is always https, but there are workarounds for that. ;-)