If you like the WordPress admin bar introduced recently, you’re going to love the way it can be expanded to do pretty much anything you want.
DigWP.com blog has a great collection of links in a single post with some very good ideas: Admin Bar Tricks.
My personal favorites are: move admin bar to the bottom of screen and disabling admin bar for non-admins.
Had no idea! Having that admin bar on the top is pretty annoying sometimes when I’m trying to preview a layout. Thanks.