Don't try to do interactive graphics with Ajax
One of the things that I think really differentiates Rich Internet Applications from traditional, Ajax-based web applications is that RIAs provide a level of interaction that Ajax just can't. Right now, because everyone is used to the browser model, we're okay with making our text-heavy applications interactive. That seems very next-gen to us because, lets face it, we're coming from HTML where the most graphical thing we can do is the img tag.
But a rich, graphical experience (done well) is inherently better than one that revolves around text. And people building Ajax applications are starting to realize that. I caught this post over on Ajaxian by Michael Mahemoff about putting dynamic graphics in the browser. The post made for a great comment by coolnalu. I can't tell if he was kidding but Michael's response addressed some of the misconceptions I see around Rich Internet Applications and Flash specifically. Coolnalu's comment:
Flash is the most powerful browser graphic platform ever existed. But somehow, there is always a voice in my head telling me not to use flash…can anyone refresh my memory on why flash is not everything we need?
Michael responds that the main argument against Flash is the user base, then goes on to list the plusses and minuses of "richer plugins".
You simply should not be trying to create a rich, graphical experience in Ajax. The options (SVG, Canvas, VML, ect) are buggy, supported in different ways depending on the browser, and, for the most part, are a poor experience for both users and developers.
The kind of rich interactivity that Flash and Windows Presentation Foundation provide are going to be leaps and bounds ahead of what any browser technology can do, and that's why they will succeed. The web becomes richer every day. Video and Music are taking the web by storm, and with the surge in broadband adoption, people are making these things part of their every day web experience. Ajax applications can't take advantage of them in the way the Flash or WPF can.
Eventually users are going to demand a better experience, one that isn't based on text and gives them the freedom to view the web they want to view it. That's one reason why Web 2.0 is so important. Technologies and concepts like RSS, tagging, wiki's and open APIs provide data in a standard, meaningful way. Once we combine this with Rich Internet Applications, users get a great experience, with loads of valuable content. Extracting that content is the first step, then breaking the web experience out of the browser and into RIAs brings it all together.
Don't waste time trying to build the next generation of the web with graphical Ajax solutions. As Coolnalu notes, you already have a solution, and it's getting more robust by the day. As your web applications start to require a more rich environment, embrace Rich Internet Applications - you'll be better off.