Bottom line? Here are my guidelines for web app design without Uncanny Valleys:
1. Do include features like drag ‘n drop, cut ‘n paste, right-click context menus, etc.
2. Don’t make your user interface look too much like a Windows or Mac application.
3. Do copy some of the common design features of modern apps, like a File/Edit menu where appropriate.
4. Don’t forget it’s a web app, and don’t try to convince the user that it’s not.