I have tried both using the at parameter and also using a X-Map-Viewport header, but when I search it does not restrict the places search to the area I specify.
For example, use the link http://demo.places.nlp.nokia.com/pla...CG24t50dHOwrLQ
This is a search near me for the word "Tokyo". There is a place called "Tokyo Cafe" I'd expect to see. When I get my results back, I get a place for the City of Tokyo in Japan!