And if your only answer is 'ads and crappy splash screens' then think a bit more deeply before you respond. People round here'd like a little bit more insight than a simple kneejerk reaction.
I think the "fear" is that once a non-web weary designer get's going with this there will be absolutely no regard for performance impact since it will render fine on what ever pimped up work station is in use.
Meanwhile on platforms with lesser hardware where the browser does not have a full hardware render pipeline the performance will likely be even worse then flash.
In fact, with the ferris wheel demo Safari eats 10% CPU time, Chrome 30%, Firefox 50% on a single core. System: OS X 10.6.8, GF 9400M.
Next thing to happen: "Disable javascript / css to save battery life on your device". :)
Im genuinely surprised that you'd even ask. Does no one see to the horror that is Flash in this things lineage? I guess not, so here's my thoughts...
First of all, don't dismiss ads and crappy splash screens out of hand. They're a cancer that the web is still undergoing serious therapy to remove. If this gains any traction, the cancer will come back, only this time it will mimic "standards" making it much harder to kill.
Content Hierachy will be thrown out the window.
We can talk all we want about web standards and accesibility, but the keystone to it all is content hierarchy. Up to now, we've never really had to sell the concept, which is good because it's a difficult concept to sell. The attraction of being standards compliant, running on iOS devices and meeting accessibility requirements was enough to create a situation where the importance of content hierarchy was ensured.
The wrong tool for the wrong job:
As with Flash, this thing will be great for some things. But as with flash, people will use it as an über tool for designing and implementing entire sites. I'm not going to list the reasons why that's a bad idea because you should know already.
Adobe, given half the chance, will push this to be a "complete" design and development tool, because that's their business. That's the type of software they make. Attempting to replace flash with HTML5 is an insanely stupid and destructive errand. And make no mistake, this is the intention.
Then there's the Amateurs, people who will forego learning the fundamentals and start knocking out half baked web sites built with this monstrosity. Dreamweaver is bad enough at enabling the talentless to inflict their creations onto the world, but this thing is going to be too much for people to resist. I'm talking about the kind of people who don't think much beyond whizz bang zippy animations. People who are essentially Magpies. You know they exist.
And then there's Adobe, who haven't made a decent product since PS6. I use Adobe products every day and have done for almost two decades. They're the worst applications I have on my system and I avoid them whenever I can. Now it looks like there will be another one I have to put up with and I don't relish that thought.
I've been designing and developing websites for more than 14 years now. I'm quite good at it too. I've worked in small agencies, big agencies, small corporations and big corporations. I spent my early years working exclusively in Flash. I believed in it, I though it was the future and I'd have fought in a holy war with anyone who didn't think flash was the best of the bestest things ever!
I was wrong. I was idiotically, stupidly and arrogantly wrong to the point of absurdity. If only we knew then what we know now.
I've seen how this movie ends, they all drown in a sea of pre-loaders.
