Ok - so after you're finished with the basic install of Joomla! and you decide that it is time to start to modify your install... this is THE single most important tool for Joomla! available. eXtplorer should be the first plugin you install after your basic Joomla! install. It is hard to believe that this tool isn't embedded within the Joomla! code itself. Manage files, templates, php, txt, html all from a single editor that has some pretty cool effects.
My only complaint (minor) with the new version is the "back to Joomla!" bar when you go to edit mode. It would be nice if you didn't actually leave the Joomla! administrator page and it just ran in a wrapper. Keep it simple.