My bud has the Windows Lumia phone and that is one killer app, she says. The one thing that pisses her off about the WP is that Google maps hates Windows.
I always use Google Search - not Bing Search - because I like Google more.
But, in my opinion, Bing Maps are clearly superior to Google Maps, and easier to use.
I do very basic map stuff, on my home PC mostly, so I'm not sure how good Bing Maps is for advanced users, or how it compares to other mobile map links.