For those looking to play with Plymouth on Ubuntu right away, it's as easy as sudo apt-get install plymouth when running on the Ubuntu 10.04 development branch. Yesterday we installed Plymouth on an Ubuntu Lucid box and recorded the video below.
Plymouth is indeed working and running with kernel mode-setting (in this video with an Intel IGP from a Samsung NC10 netbook), but it isn't too exciting at the moment. Ubuntu doesn't yet have any striking artwork for its Plymouth plug-in or anything beyond a static Ubuntu logo. Right now there are also many udev warning messages bleeding through the screen and it isn't as tightly integrated with the GDM / X.Org Server at the moment compared to Fedora with its nice fading transition.