Rajat Pandit has put together a bookmarklet for YUI Logger that allows you to pop open a logger console on-demand — a big convenience when you're debugging. Check out Rajat's blog and bookmarklet page for more on this project.

Keep in mind that the YUI Logger Control outputs messages logged via YAHOO.log; to see full YUI debugging messages, you'll need to use the -debug version of YUI files. For example, to use the -debug version of the YUI Event Utility, use http://yui.yahooapis.com/2.5.2/build/event/event-debug.js.