I dont know what ya'll are talking about. It's more than possible make your js app crawlable by Google. Just use HTML snapshots if you want to do it by hand, but I use this because I'm lazy, http://seo4ajax.com.
Actually, it's just incredibly bad technical advice to just dismiss js apps like this.
If you're creating a service that doesn't sit behind a login, use javascript sparingly. Why do you need a full-blown search/filter function on a production or information landing page?
Make it basic, and then have the results pop up via AJAX. Sure, you're losing SEO value from those search results, but you can create a table that basically shows that a user went from page ID 123 to page ID 234 and you can populate a list of 5 'articles' that people may be interested, based on searches. That list output should be generated server-side and really should be cached for a day, and there is your lost SEO value from search results which is going to actually help more in the long run.
I think it's great that we can easily re-create any type of website we want to using a javascript MVC, but it doesn't mean we should.
That being said, if SEO was a big deal to me, such as when I create an e-commerce site, I would use progressive enhancement and some of the semantic-web enhancements to describe my content because sales drive development. I've done that in the past successfully. But I've also just finished an entirely JS-based single-page-application because we didn't need SEO, as everything was hidden behind a login, like facebook.
My point? I don't think one size fits all, yet.