Aside from plymouth-set-default-plugin, the other Plymouth binaries include plymouth, plymouthd, and plymouth-log-viewer. The plymouth executable is used for configuring the Plymouth Daemon (plymouthd). Plymouth can support prompting the user for a password and sending it to a command, whether to retain the boot splash on exit, and other options. In addition to Plymouth being a nice KMS-driven graphically pleasing boot experience, Plymouth logs all messages generated during the boot process. Once the system has booted the log can be viewed using plymouth-log-viewer, which is a simple GTK window. Alternatively, the boot messages are logged to /var/log/bootmessages.log by Plymouth.
For those that don't have graphics hardware that supports kernel mode-setting, Plymouth will fallback to using a text mode progress bar or the displaying the detailed messages. Plymouth does also support using a VESA frame-buffer (vesafb) by issuing an additional argument from GRUB (using vga=0x318). Right now the ATI R500 and R600 (Radeon X1000, HD 2000, HD 3000 series) is what's working well with kernel mode-setting on Fedora 10. Previously the Intel driver had worked well with KMS on Fedora 9, but due to major changes including the Graphics Execution Manager and other invasive work, the KMS support has fallen behind.