Excel Mashups

This is the first interesting thing I've seen Microsoft do with Excel on the web. Who is using it?

I'd like to see a demo on the site, and there isn't one.

Without wishing to belabour the obvious, this could be huge. Excel is probably the most popular development environment in the world.

This has actually been a part of Sharepoint for the last few years. It's called Excel Services (http://msdn.microsoft.com/en-us/library/ms517343.aspx). It's very clever that they extended it to SkyDrive.