I've put together a little bookmarklet that lets you use OSM maps on Google maps and Multimap API implementations (and in fact multimap.com). In fact I updated it today and have a new blog post about it here.

It can be really useful when you find a site that has useful data but you want to see that data overlaid on OSM maps. On Multimap's site you can also see routes and lots of other POIs overlaid on the OSM maps too.