so what i can tell you so far about Lubuntu, is that it looks pretty slick.
It comes with Chromium (the Open Source version, not the Google Version) as its default browser, MPlayer and Aqualung as its default media players. Sylpheed for Mail. Abiword/Gnumeric as its default Office Apps. Pidgin/XChat for IM and IRC, Transmission for Torrents.
It uses Openbox and LXPanel. at least I think it is LXpanel. only one Panel, on the bottom, as opposed all the other 'Buntus that have 2 Panels.
the Iso is 380MB total.
its in Alpha 3 right now, so naturally some things don't work (like auto mounting) and will change before April 29th when it will go live(some of the current packages will be replaced).
Lubuntu in specific, and Lucid Lynx in general are shaping up to be really nice from what I can tell.