Storing Droppable positions

Hi Guys,
I'm in the process of developing a user portal, i am using the
"Droppable" feature from jquery, my question is once the user has
dropped the panel to whereever, they want it to appear on the page,
how do i go about keeping the panels in the same place (instead of
reverting back to the default location on the page), for the next time
they login?
cheers guys
andy