Okay now we're pretty far off topic but I'll continue the thought here... AJAX as stated has huge appeal because of it's flexibility. You can take any HTML developer, anyone with a basic coding background, and any web designer, and migrate them from working on traditional web development into the AJAX scenario with as much, or as little, "rich enhancement" as you want. Same story goes for performance and devices; you can have a lot of very basic AJAX techniques that make a website soooo much easier to use, especially on things like mobile devices, without incurring a lot of overhead. You have the ability to go all out ape crazy too, but those aren't the majority of cases that you run into. And thanks to web standards cross device cross platform issues are pretty minimal.

Flash has it's uses, and even in the AJAX paradigm it can be handy for doing things that other technologies aren't as well suited for; at the moment video handling, things like socket connections, etc. The problem with Flash generally is two fold: 1) developers and people who use it subscribe to the "flash or nothing" mentality typically. Because you have to learn to use a whole new methodology of authoring and developing, you end up trying to use Flash for more than just what's it's really good at, which adds overhead and in the end a reduced user experience. 2) The flash player is horribly inefficient, especially on mobile devices, simply because it has always been designed as a high level runtime. And the problem here is that it's inefficient because you incur the same base level of overhead whether you have a flash movie that's just a green blinking dot, or a whole interface, because the player still has to load up and process the swf. Now obviously more complex swf's can require more memory or CPU cycles to deal with, but the point remains.

Anyways enough of that... as I tell my students (I teach AJAX development at a local college), it really just comes down to the best tools to do the job; only incur the overhead of Flash if you actually need the features of Flash and you've already got a Flash background.