I know addons aren't coming until Version 2.0, but I remember in this old interview on Blue Gartr from four months ago, SE said were planning on making addons use Adobe Flash since it was more visual than straight-up coding. Now I've got nothing against making things more visual, but using Flash is not a good idea because it eats up a ton of CPU power needlessly (this one of the biggest reason why Steve Jobs hated Flash and Apple is trying to kill it).
Not to mention that even with Flash, you'd still need to know how to code to make a decent addon, anyway.
Basically what using Flash would mean for the end user is that we wouldn't be able to load nearly as many addons as we can in other MMOs, and the addons we did have would be much more likely to cause lag and memory issues. That's not good.
So while I can appreciate and understand SE's desire to make creating addons more visual and user-friendly for players, I don't think the high cost in CPU power can be justified, as it would make actually USING addons more of a headache than it should be.
So please reconsider using Flash, SE. The price isn't worth it.