What is the commonly accepted way so an admin can set panels/widgets positions (i.e. from the image below, set “Data Finder” to sit on “top left”) ?
In other words, the customer/admin would like to be able to configure the widgets/panels positions at startup (and users see that by default), maybe using a JSON configuration file that is easy to edit?
I am using YUI 2.7, but other frameworks solutions are welcomed.

portoalet,
Using YUI 2, I’d base the project on the Layout Control and — as you say — have an admin page where the admin can set her preference. If you’re not using progressive enhancement, a JSON config file would allow you to write a handler that sets up the layout according to the user’s preferences.
You might also want to look at the portal example for other ideas about building full-page apps in YUI 2:
http://developer.yahoo.com/yui/examples/layout/adv_layout.html
Regards,
Eric