I am in the process of working on something similiar myself. I have written an application currently called "CarConnection", which currently loads up and uses mappoint. It has a little map in the corner and goes to your current location and tracks you as you move (Basic GPS location). It constantly updates your address and I use the postalcode. It has 4 major buttons on the left.
I wrote it in C#. Currently I pull traffic images based on zipcode from http://www.sigalert.com. This is only a source for California traffic though. I scrap all my data and images from there. I use msnbc and weather.com for my weather information. I based that logic on MythWeather (a linux weather program for the Myth PVR system) The email client I wrote in C# and its embedded. The Web Search just goes to google and allows you to use the virtual keyboard from VOICES. Anyway... Your idea sounds awesome integrating the pushpins into Mappoint. I can prolly help give you a reliable source for California data. I should have a beta of my software in the next week also, for people who want to play around with it.