You can do something similar to what you are trying to achieve by using the Object "Patterns". On the object properties choose the field tab, then click the patterns drop down. Or you could use some javascript for the onSelect event.

You are correct. I have not tried that method nor read much about but i do now recall reading about the feature being available through acrobat pro somehow. I am not sure if it will work for reader users? Im not sure also which book i have that discussed that option, it might be the book by j.p. Ter...

let me specify a bit more, it is software you buy and install on a machine, then you use the web interface of the software to enable features for your form. then when you distribute it to users they will have the ability to save the form with the data they entered. Hope that helps you.

You have to have Adobe Livecycle Reader Extensions. It is additional software from adobe that you purchase and install, it gives you the ability to enable a form filler to save the form data as entered.