When I first joined Microsoft, I was sent to help build an application for a large telecommunications company which had some heavy-duty mapping requirements. This app needed to enable the display and design of undersea fiber optic cable networks. I had just been through my new-employee training, and thus had the following guidance and support to fall back on:
"don't mess up"
Fortunately, I had a really great UX designer to work with, and even more fortunately, I had a good friend in the GIS business with a powerful ActiveX control that was just hitting its beta cycle. After about 9 months of intensive development to get all the clicks, layers, and transformations right, the result was an app that met the above requirements and enjoyed several good years in production (it might even still be in use.)
I later got to work on a GIS application (for the same telecommunications company) which connected maps to OLAP data, and had my first encounters with plotting geo-coded points on a map. I'm not sure if this app survived the telecomm meltdown earlier this decade, but it did at least enjoy a couple good years of production usage.
Since that time, I haven't had any GIS applications to work on, so I stood on the sidelines and watched the remarkable progress made by software industry in bringing interactive mapping into broad usage. I think it's time to get off the sidelines and back into being a GIS programmer.
Tonight, I registered for a MapPoint Web Service developer account (from the form on https://mappoint-css.partners.extranet.microsoft.com/MwsSignup/Eval2.aspx.) While I wait the 1 to 2 business days to receive my key, I'll have to satisifed with reading through the SDK documentation and samples (no, I don't get out much, but this is as good as it gets for me on a rainy holiday weekend.)
If you're an ISV looking to add features that could differentiate your products, I encourage you to check out MapPoint and Virtual Earth - there's quite a bit there, and it looks quite easy to implement and integrate. Just be sure to get your developer key before you try to get started.