If you want a simple Plymouth manager to easily change, install and remove Plymouth themes, try the the new Zorin Splash Screen Manager.
Installing the proprietary Nvidia or ATI graphics drivers in Ubuntu (10.04 or 10.10) will make Plymouth (the boot screen) look very big and ugly. The script in this post should fix this.
Kubuntu just got a new Plymouth theme [...]
Sorry for the many Ubuntu updates today, but since it's the UI freeze, most of the artwork comes today.
I've finally got Plymouth up and running on Ubuntu Lucid. Here is a screenshot of the Solar Plymouth theme: