The real problem with this, is that soon advertisers will start making canvas ads instead of flash ads, and then what have end users really gained?
The reason that Flash is hated is mostly because it's been misused. And now it will be easy to misuse HTML5/canvas too.
We can now use Javascript to do the same stuff that flash could for many years. Don't take me wrong. I love programming in javascript, and I like that I can now do these things. But what do normal, non-programming users get out of this? That they don't need a plugin? I'd bet most normal users doesn't even know what is flash and what is not. And the way I see it, the canvas-renderer isn't somehow more magic than the flash-engine. Except that it's built into the browser, but you could argue that you could just as well do that with Flash.