I am assuming you know how to write a WordPress plugin, and now you are wondering how to use ajax to add that sexy feature that will make your plugin look a bit kool.
I faced the same problem, with my akWpUploder plugin. I googled but could not find anything interesting, or should I say, simple way of adding ajax to my plugin. So I dig into the WordPress code base for solution, as auto-saving feature of WordPress was one such thing that I wanted to use.
There I found what I was really looking for, a very simple way of using Ajax to get things done.
Problem: How to use WordPress functions in your plugin when using ajax
Let me explain the problem first, while I was working on my plugin I needed to insert the photo data into the database. To do this I needed to use WordPress database functions, but the way I knew to use ajax(i.e. creating a separate PHP file that handles the ajax request), it was bit difficult and messy. It would have involved either making a direct connection with the database or including the WordPress config file.
I was not happy with either of these options, I needed a simpler solution.