I've not read this entire thread yet, so if this redundent, sorry.
Im working on an mod to the Topic Description mod and AJAxing the tooptips that allows previe of the first adn last posts in a topic. If there ever was an example of using AJAX, this is one.
After trial and error of different tools, learning curve, etc I'm on track with a working solution, not without need for more work.
Im using these open source tools:
AJAX support (based on Rails)
Bing used for Event/Presentation but is really a package of cool stuff(more Rails)
I wonder where we might end up with different mods using different helper packages. Probably not much we can do to aim toward standardization.