an ajax widget i like
I don't like much that's done with AJAX because it's usually too much. If you change half my screen then you should really just be reloading the page. However, Mike Davidson has done a little polling widget for inside blog posts which is great. A perfect use that's instantly and obviously superior to other polling systems that have popups. A poll is a small ancillary piece of content to the blog post itself that doesn't need it's own page refresh.
http://www.mikeindustries.com/blog/archive/2005/08/the-polls-are-in