Now this is a hard question, I know, hence the big points bill.
As a user of Internet, I have seen many, well designed dynamic forms, while others are truly terrible.
Many pages I've seen don't use this technique, even Experts Exchange has a better solution: when I click on the "+" near "Web Languages" the list of sub-topics will appear instantly, without reloading the page.
Now, given the fact that I want a code which will load only once, and that eventual, run-time modifications of the page will happen without further re-loads, which technology should I employ? Applets? JSP? Even, say, Flash forms?
I am very interested about your opinion and experience.