First of all, Bing's iPhone app is big news for Bing.  It signals a number of shifts, principle among them A) strong recognition from Microsoft that they aren't ignoring non-Windows Mobile phones, and B) this was Bing's first significant functionality leapfrog over Google.  Leapfrogging Google is a big step towards gaining search traffic from the category leader.

What I Like

• The interface is simple and stunning
• Have I mentioned that the app is beautiful?
• The app brings the character of Bing to the mobile, complete with the information rich and stunning wallpapers.
• Strong visual search.
• Integrated voice search.  I still can't believe Google doesn't have this on the iPhone.
• The search (like Bing.com) often knows what you are looking for.  Weather pulls up the local weather, not just weather sites.  The same cannot be said for locations and maps.
• Visually clear and rich directions and map data.

What Needs Improvement

• Search is still Bing search, good for some things, not for others.
• Maps needs an overhaul.  Some of the flaws listed below are flaws in the maps product overall and do not reflect a significant change for the iPhone.  Nevertheless, it impacts the user experience.Maps doesn't come close to Google's Android product.  Bringing a product at least on-par with Google's Android functionality to the iPhone would have been a real door-buster.  Here are some basic flaws:
• • POIs and intuition are weak - It didn't recognize CitiField in Flushing, NY or JFK in NY as POIs.
  • Maps needs to include compass functionality for true in-motion turn by turn directions
  • Visually, traffic wasn't too easy to see behind the lines of my route.
• Much like on Bing.com, the search does not intuitively know when you are looking for directions.
• I would love to see stronger tie-ins to image search using the camera, potentially layering in any of Microsofts many photo tools.  How cool would photosynth recognition (by GPS), uploads and viewing be on your iPhone?

That being said, this is a first release, and a decent first shot.  Looking forward to seeing great things in the days ahead.