User participation is one thing, and great for the developer which has built and is growing its audience through the successful implementation of a bright idea. But underlying the peace of mind of that developer whose audience is based on the successful merger of others' bright ideas in a mashup must be the assurance that the owners of its contributing APIs do not change the terms in their licence. This is certainly a pre-condition for any developer wishing to add commercial features to a successful site.
Essentially, Mapstraction's aims, if successfully realised, will provide commercial site developers with insulation against the whims of the big guys, not all of whom can be expected to do no evil when they begin to see big dollars rolling into someone else's pockets on the back of their own innovation.
Mapstraction also claims that it will seek to fill the holes in the offerings of the current giants. Moreover, it will work with the OpenStreetMap, a "free editable map of the whole world ... made by people like you."
An eminently sensible idea, its development roadmap can be found on its site.