Adrian, good post, and overall very postive about Orbeon :-)Just one precision: Orbeon does not use Dojo, but YUI. But if I may ask, why do you say Dojo is the worst possible choice?-Erik (Orbeon developer)
Thanks for pointing out that mistake. It is Chiba that uses DOJO, not Orbeon. I put that sentence between DEL-tags. It is nice to know that Orbeon developers are reading this blog by the way!
I must admit that it is not a nice thing to say that DOJO is the worst possible choice. That is an opinion and depends on selection criteria. Your mileage may vary.
For me, there are two reasons why I am not fond of DOJO.
1. Its size: The full DOJO toolkit is 4.1MB compressed, 19.2MB uncompressed - compared to 16KB compressed for jQuery and 97KB uncompressed! Even though you might not use the full DOJO tool set and even though they do offer a 23KB compressed core, the usage of large libraries is not my taste.
2. IFrames. Where XHR is unavailable, DOJO tries to fall back on IFrames. It is worth a separate post to point out the disadvantages of IFrames. The main point here is the possible security vulnerabilities.
Personally I prefer JQuery. Here is a set of slides that introduces jQuery and how it follows the principle of Progressive Enhancement rather than Graceful Degradation:
It also mentions YUI and DOJO on slide 47.