I rarely step into these web browser fights but in this case I'll make an exception.
Let me start off by saying I support whatever works, not any company, technology, etc. However as of late, I mostly do Flash/PHP development. I do love javascript,and the simplicity of a CSS, HTML environment, but I'm obviously still biased. So I'll break this down into three sections.
1. Why we hate Flash.
a) We hate Flash because it attracts the worst of developers. Many of these people, have no prior experience in web development and want to see something and make something the same way millions of users sign up for blogs and choose a pre-made format. As a UI designer and programmer, I know that 90% of people are not meant to develop user interfaces. This sort of development is significantly more complicated to do well then most people realize.(And I am not talking about making a simple tabbed out, div based css vertical scrolling website that make up most of the web.) I'm talking about understanding true user interaction and figuring out custom solutions to user interface that don't break the public's established web perception and still offer. When Flash gives you the tool to make everything how you want it to look, most people are bound to mess it up. This is and is not Flash's fault. If Flash were to disappear and be replaced with something else "easy" all of the terrible designers and developers would flock to the new hated format of the web.
b) It's a resource hog. I agree, that it is but until someone find me a way of doing all of interactive multimedia features of flash, including interactive video, 3d interactivity, physics, and animation, I might have to say it's irreplaceable.( And yes you can use all of these things subtlety without making a mess).
Also this will most likely change, whether it's with Adobe's new player coming out (currently in beta finally offering full hardware acceleration and GPU support) or in newer versions.
c) Myths...Flash breaks the back button, Flash doesn't get search engine indexed(ah the mythology of SEO)....SWFObject and SWF address are two wonderful javascript additions handle these problem pretty well(nothing is 100 percent but still...), and SWFaddress also has javascript support as well for the same issues. I'm not an expert and I don't claim to be but I know I can make a Flash site that has interactivity you can't get anywhere else in one package, and supports all of the standard advantages of HTML CSS so much so that on most* computers you would have to check the source to see if it was Flash. And I'm no expert.
2. The war ...on Adobe*cough* I mean web standards...
Is Adobe a company set on making a profit by any means, however cunning? Yes. Duh. You knew that. So is Apple, Google, Microsoft and the self-touting open source companies you love. It's widely known Flash is Adobe's 'trojan horse'. But why do we want standards? So everyone can access the most information the most efficiently with transparency and freedom for all. Yeah that's what we want but are these standard giving us features to get the speed and compatibility or just telling us to forget about them. Also do companies want open standards for the good of all? Apple wants their software(quicktime player, etc) and languages everywhere so they can run their hardware fast so people buy more of their computers and make your iLife complete(This might be a good time to point out I am an apple fanboy with multiple macs), microsoft wants the same(replace software to better running hardware to dollar signs with just straight dollar signs) and google simply wants the web everywhere and to replace software with web software entirely. To what end...I won't even get into that one. I'm not trying to make all of these companies sound evil but they all want to succeed, to thrive. So some of these things are in some way in their plans even if I sound overly dramatic.
3. Sproutcore's potential or not?
I don't know if Sproutcore is any good. I looked quickly and wasn't impressed. I think other tools like Jquery and others have far more potential than this sproutcore. I find it suspicious that apple backs javascript so strongly and has such a great relationship with google when I still can't get my brand new(uncorrupted by clogs, and time) mac pro's safari to load gmail consistently without failing, despite google's best efforts to fix the problem. I know, I know, a new javascript engine that is much faster is coming to safari 4. Just don't forget that if you turn off Flash there are other people who also turn off javascript. It's only one click away from that Flash disable button. If you do this you may not be the average internet user.
In the end I'd love to see and open source multimedia rich internet experience that can natively be supported by any browser but until HTML and CSS do more than simply act as placeholders for real programming languages I might have to stick with Flash's current penetration( at least 80% though I know they say nearly 100% on their sites) and rapid development capabilities. If someone can direct me to that tool, I'll gladly look into it. But just remember it has to be able to give me HD video, 3D gaming, full database/ASP/PHP access(not necessarily built in), rapid prototyping(the list goes on) all in one IDE and someone to teach me to use it!
Remember the days before Flash and how awesome everything was and how much everybody loved all the sites that emerged from those days~ These issues migrate, they don't disappear.