What's the best javascript library, or plugin or extension to a library, that has implemented autosaving functionality?

The specific need is to be able to 'save' a data grid. Think gmail and Google Documents' autosave.

I don't want to reinvent the wheel if its already been invented. I'm looking for an existing implementation of the magical autoSave() function.

Auto-Saving:pushing to server code that saves to persistent storage, usually a DB. The server code framework is outside the scope of this question.

Note that I'm not looking for an Ajax library, but a library/framework a level higher: interacts with the form itself.

daemach introduced an implementation on top of jQuery @ http://ideamill.synaptrixgroup.com/?p=3. I'm not convinced it meets the lightweight and well engineered criteria though.

Criteria

• stable, lightweight, well engineered
• saves onChange and/or onBlur
• saves no more frequently then a given number of milliseconds
• handles multiple updates happening at the same time
• doesn't save if no change has occurred since last save
• saves to different urls per input class

Updates

I've stabilized a solution. See my answer below for links.