I have to show this off... AJAX Inline Comments
I've always had inline comments on my blog, so that on the front page you can click "show comments here" and it will use JavaScript to reveal a hidden DIV below the entry that contains the comments. The problem with that is that all the comments for all the posts on the front page are loaded when you load the front page, which makes the page longer to load (more queries) and longer to download (all those comments!)
So, my solution was to use AJAX to download the comments as needed. That is, when you click "show comments here," it downloads just the comments you wanted to see.
Also, I used Moo.fx effects to fade and "slide" them in and out. Let me know what you think.
NOTE:
NO, I CANNOT make this into a plugin. It simply requires too much theme editing. Of course, if you wanted to hire me to do it on your blog, I'd be happy to oblige. :-)