Google Apps does have some very handy tools, I agree that their are certain cloud based apps out there that do excel.
I just don’t see a web based CAD system as successful, at least not in its current form. If you can figure out how to incorporate the Ruby API and support plugins then it might have a chance but my suspicion is that its performance might suffer especially if it is somehow too dependent on the users internet connection.
Taking all of SketchUp to a web based app is utter silliness in my opinion. I always say don’t fix what isn’t broken. What does SketchUp stand to gain by taking their flagship product from a stable desktop app to a cloud based app?