I had a chance to install Ubuntu's development version, Breezy, on a spare hard drive this week. It's almost ready for release next month: everything seems to be there and working well (but the daily updates are occasionally still slightly broken).
The system looks great (switched to the Clearlooks theme with Human icons, that's all) and runs fast. USB devices get detected, mounted and responded to as they should do; the new Nautilus view is perhaps the best file browser ever (a combination of a tree pane, informative icons and a breadcrumbs-style navigation bar goes even further than the best bits of both OS X's Finder and Windows' Explorer, but the actual functionality of Nautilus is still pretty basic). Beagle, VLC, Muine etc are all there and working better than ever; the (non-Ubuntu) installers for Java, Azureus and RealPlayer do their job; Totem has an integrated playlist view; and I got wireless/WPA working again with a bit of tweaking (will post that later).