How to build an in-page checklist that auto-saves user input?

Hi all,

I'm putting together a collection of exercises for users of my addiction-recovery site (finally getting back to my pet project!).

I'm building a page on which all available exercises are listed with a checkbox next to each that can be checked when completed. What I'd like to accomplish is to have the logged-in user's data saved so checked boxes are still checked the next time the user logs in.

I know there are oodles of form-builder plugins out there, but I don't want my users to have to click a "Submit" button (then get a "Success!" message or be redirected away from the page). Simply check the box and it stays that way... unless unchecked, then it stays unchecked.

Can anybody clue me in on how to code this type of feature? My mind is kind of foggy today ;o)