I just finished switching an implementation of Google Maps over to Bing Maps. We used Google Maps to display a list of locations to choose from, centered on your current location. It was working great until we had to deliver over https. The only way to get Google Maps to work properly (without some sort of proxy hack) is to get the Google Maps API Premier which costs a lot of $$$$. Opening up in a new window or an iframe wouldn’t work due to browser restrictions.
So, after giving up on Google Maps, I pulled in the Bing Maps API SDK, and rewrote the entire code for the map locations. It took about 1/3 of the code that Google Maps API v3 used to do exactly what I needed. And instead of having to fork out a tonne of cash, all I had to do was change the http in the script src to https, and add &s=1 to the end of the URL. Simple, quick, and works.
Also, I haven’t really tested this a lot, but my impression is that Bing Maps just works better. It loads faster and seems to be more responsive.
From an end user perspective, I tried to use Bing maps to find nearby places to eat and it failed miserably. I found Google much more useful for that sort of thing. This is probably one of those scenarios in which I was not patient enough with the new thing.
I do see many more sites using bing nowadays however. I do prefer the interface and it does seem much more snappy.
The lincencing is also drastically different for Bing maps though. They have much lower limits of number of views, etc. Also, with Google Maps those limits are for your end users.
With Bing (I think) they are tied to your API key.