That's ok as a rule of thumb when you are talking about a chalkboard project. I agree with it. But there's a running app here. You can measure user experience based on experience. From my 2 minute play & the comments here. Seems ok on that front.

If that copy/paste/ font sizing etc. bothers you here specifically, then it's a point against.

javascript is far more widespread than flash

I'm not sure how much non pc browsers are going to have a need for this anyway. screen size etc.