Website Insight is an excellent tool, I've been playing with the trial today. But as someone that develops sites from scratch locally before uploading it would be really nice if it could also test sites running locally (http://localhost).
So glad to hear that!
Because many aspects of the program query services that are online by passing your URL to them, scanning files locally would prevent those from working. We would have to basically disable all features except the Components, Insight and Keywords Tab(s).