Old now, but done as a proof of concept in using browser local storage. Not long after, a vendor tried to sell us a near identical product for doing these nots with Salesforce back-end storage. So I adapted it to do that too - didn't need the vendor.
Anyway, here's the original version for you to play with. It uses a light wrapper library to handle the storage. I know note placement on screen isn't quite random enough, have fun fixing it :)