Foursquare is working on a venue harmonization map that does this. See: http://blog.foursquare.com/2011/03/14/1up-the-importance-of-...

This sounds like YQL, e.g. http://developer.yahoo.com/yql/console/?q=show%20tables&....

I think it comes down to marketing. I did not know YQL offered proxy access to all those APIs.

They don't proxy, they add edges.

For our startup, we are matching place ids to different services which includes Yelp, Facebook Places, Google Places, and Foursquare.

We plan to make this publicly available thru an API when we have thousands of places matched.

See also: http://www.TheEasyAPI.com

Quick note for OP - I got two copies of the signup email after signing up