The point Dave makes in the original post, is that he sees new flash content being produced, so the boycott is not working. I think it is more productive to focus on promoting html5 to make flash irrelevant.
I ran Debian on a PPC machine a few years ago so I couldn't use Flash. Back then only very odd setups like that didn't have it. Nowadays millions of people are buying new top of the line devices that don't support it, so the tide is turning as a result.
If Flash will eventually disappear it will be slowly, very slowly. Companies are reluctant to get into new technologies. Has DVD disappeared because of Blu-ray? Has Windows XP disappeared because of Windows 7? What about Internet Explorer? And it's the same outside of the tech industry too.
Some sites will be early adopters, some will be slowpokes and most will be somewhere in the middle. And in this last year we've seen a _lot_ of mindshare being gained by HTML5. For a start Youtube, Vimeo and friends. Let's remember that a couple of years ago Flash was basically had the whole market by itself.
I don't know if the iPad/iPod helped, but I do know that Flash is starting to lose its grip. And yes, of course people will still develop on Flash for many years to come, the same way some companies were still selling VHS players a couple of years ago. But the adoption is gaining steam.
So there's going to be stuff done in flash to appease the designs of sites. But once HTML is more mature, and people know how to use it, they're not going to do the work twice anymore.
Make no mistake, having a major platform like the iPhone/iPad is pushing that forward. It's hard to tell how or when this will turn out.