We can probably all agree that jQuery is pretty awesome. It makes writing client side code a piece of cake and there are tons of plugins to do what you need or at least to get you started.
But with all the plugins, comes more code you need to debug if you need to tweak or modify the plugin. Recently, I used a plugin that converted a bunch of check boxes to a multi-select dropdownlist. In the background it added several new DOM elements to the page and attached events. I needed to intercept a click event but I didn't know which of the many elements it was attached to.
*Visual Events works with other frameworks as well. But I have an affinity towards jQuery :)