Unfortunate that Mozilla's the only one to still get this right. I mean, in the test, the missing image is pretty big, but when it's smaller than your alt text, everyone seems happy to cut that text off (except, Mozilla). It's actually one of my reasons for sticking with this bloat-browser.
So far I've only been using it in forms/form controls.
But it would probably then work best with your examples where there's a link involved (like from the example 2.2 at w3.org)?
I'd consider it widely supported, at least some things. browser support test
It also depends on the reader. They're expensive to update (the big commercial ones I mean) plus Window-Eyes seems perpetually behind everything new recently. But most of the last several versions of JAWS, NVDA and Orca have ARIA support. Not sure about that SAToGo thing, I've never touched that one.
So yeah I agree with you it should be a supplement today. But do use it!
What's after the images? Just more text?
Screen readers have all sorts of ways to navigate, though Gonz (Chris Hofsteder) was telling me not too long ago how sadly normal it is that many screen reader users never seem to learn to use all the possibilities of their tool. Meaning, that there are a lot of people still using Tab and whatnot. That would drive me nuts, because you can move about in so many ways (best if the page is structured well of course). It's kinda like we can do all sorts of things with browsers, like enlarging text, while the people who would love that most (like seniors) tend to be totally oblivious to these abilities.
Certainly screen readers would be kinda worthless if your only real option in most cases was to sit through and listen to everything linearly.
I mean, if I see a chunk of junk, especially if it's a long bunch of links, I'll N for "next Non-link text" for example. But I was lazy enough that I wanted to learn the quick-keys.
Orca locates "objects" and you can choose to just jump to the end of an "object" if you want. (A list of links can be treated as a single line, so one down-arrow and you're out, for example)
You can also add aria landmark roles around the page too. Yeah, the HTML4/XHTML validator will whine at you. Whatever.
I'm personally conservative in my skip links, but depending on how your page is structured it might be a good idea.
Using keywords for your "alt labels" is probably also good, though do you eventually start getting church1 and church2? : ) But yeah I like that better than image1, 2 but I've also seen image galleries where the caption has a date in bold, then descriptive text in normal type.
<p><span>5 Dec 2011:</span> The kids were excitedly waiting for Sint and Piet</p>
where the date, if unique, would be great as an alt label.
I can haz shortcutz? : )