It will still be unacceptable for development purposes because of the poor quality of their utilities. Does this affect non-dev users? I would argue yes, because web apps will have the fewest bugs and run the best in the browser they are developed in. All work done to make the app "cross-browser" will be blamed as compatibility issues with other browsers. This is why IE, no matter what version, will always be seen to have compatibility issues (unfairly in my opinion - IE is a fine browser and all browsers have some differences) until it has development tools on par with Firebug or Chrome.