it's a great idea - much better than the old built-in formula dependency tracker. definitely loving your idea! I've been in the Excel business myself for years (having worked in finance) and always love when someone comes up with a fresh tool for the mighty Excel (yeah, I know most developer's views on Excel...). I've recently started www.spreadgit.com which is a GitHub-like service for spreadsheets. looking forward to playing around with your service!