For the past couple months I've been running an experiment of sorts where I had Firefox set up to block Flash by default, and then I'd selectively enable it for sites that needed it, like YouTube and Vimeo and Facebook and so on. I've come to the conclusion, yet again, that the sites that I visit are still a long way from being Flash-free and HTML5-friendly. Not only was it obviously obnoxious for Flash content that I wanted to see like videos, but there were a lot of unexpected place where it sucked, too: some sites have transparent Flash ads that cover a significant portion of the page, and with Flash disabled, parts of the page were simply inaccessible. And some sites that I visit a lot like Soundcloud have script on the page that interacts with the Flash content that didn't know what to do without it. And there are cases like where YouTube has a Flash-free beta player but it's pretty broken and isn't as functional as the regular Flash one.
My first experience in recent years with a Flash-free world was with the iPad; that was a couple years ago, and I found a lot of things frustrating about the iPad but the lack of Flash support was a big one. I don't actually even completely remember what motivated me to try living without Flash again other than pure curiosity. Microsoft decided that for the Surface, Flash was still a necessity, and right now I feel like this "experiment" vindicates the people who made that politically awkward decision pretty well.
I'd love a world where Flash was not a requirement to browse the web, but as far as I'm concerned, that's still going to be a while. People like to talk about how everything's HTML5 now and Flash isn't necessary, but either those people visit a wildly different set of websites than I do and never click on random links from their friends, or they're just deluding themselves.