Microsoft’s answer to Google Maps due this summer. I’m downloading the 127Mb video right now, and hoping it’ll be decent enough quality to get a good feel for what’s to come. Since a good deal of interest in Google Maps seems to have been through its hackability (although I don’t imagine they planned that), I hope that/wonder whether Microsoft will include some kind of API for custom datasets. If so, look forward to an enslaught of third party overlays and datasets.
If you’re a Firefox user it’s well worth reading this link and taking the appropriate action – Secunia think it’s rather serious.