This bookmarklet will flip between Google Maps & Bing Maps:
 
javascript:%20var%20_cur=%20""+window.location;%20if%20(_cur.search(/http:\/\/maps.goog/i)%20!=-1)%20{%20var%20_url%20=%20document.getElementById('link');%20function%20gup(%20name%20,%20u)%20{%20name%20=%20name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");%20var%20regexS%20=%20"[\\?&]"+name+"=([^&#]*)";%20var%20regex%20=%20new%20RegExp(%20regexS%20);%20var%20results%20=%20regex.exec(%20u%20);if(%20results%20==%20null%20)%20%20%20%20return%20"";%20else%20return%20results[1];}%20lurl%20=%20'http://www.bing.com/maps/default.aspx?cp='%20+%20gup('ll',%20_url).replace(/\,/,'~')+'&lvl='+gup('z',%20_url);%20void(window.open(lurl));}%20else%20if%20(_cur.search(/http:\/\/www.bing/i)%20!=%20-1)%20{%20eval('var%20_xxx%20='+%20document.getElementById('MapControl_MapControl').value);%20gurl%20=%20"http://maps.google.com/maps?ll="%20+_xxx.C.Latitude%20+","+%20_xxx.C.Longitude%20+%20"&z="%20+%20_xxx.Z;%20void(window.open(gurl));}%20else%20{%20alert('This%20script%20only%20works%20on%20maps.live.com%20or%20maps.google.com,%20check%20http://dev.robertmao.com%20for%20update.');}