I came across an agency claiming they produced accessible Flash today, they go by the name of DDX. You can read about 'DDX Flash SEO' on the HTML version of the equivalent Flash page.

Here's what they say:

Accessibility
View your content on mobile phones, screen readers and other text based browsers.

Judging by their full-Flash, low-contrast, slow-loading website, I was doubtful.

jQuery's .html() function is frequently used to read and modify the contents of a page, unfortunately is uses innerHTML for this. innerHTML is evil for a number of reasons; mainly it's poor support in IE and inconsistent output across browsers

To illustrate this I've compared jQuery's .html() output, and that of innerXHTML which reads and writes clean XHTML reliably.

See the test in action

The Results

Sure enough, we get some problems with jQuery (innerHTML) in IE:

glo-stix - Threadless T-shirts, Nude No More
My Threadless.com Submission

The crap HTML provided by Threadless for these 'submission banners' does annoy me. Inaccessible, non standards-compliant and practically useless...

What can be done about it? An API would help, in lieu of that; maybe some source scraping could do the trick until they find the time.

What's the worst possible type of website to present with Flash?

Something text heavy, with frequently updated content, that's only success depends on Google indexing and links from other sites.

How about a Flash blog?

Replicating the particulars of html based presentation, while removing functions that people have become accustomed to;
like opening links in a new tab, downloading images, copying text, increasing the text size, ...not to mention accessibility

Genius!