Well one thing I've noticed about plymouth is that it seems to handle multi-display scenarios better than it used to. It used to do stupid crap, corruption, blinking, etc., when transitioning to GDM with multiple displays. Now it fades smoothly across all displays. First time I noticed this was after updating to F15.
Just had hard time trying to make Plymouth work right with SystemD (I'm using NVidia blob driver) on Arch Linux. I've finaly been able to get a splash after I reinstalled it using the Aur package Plymouth-git-systemd. I however have to press F2 on boot because it doesn't kill plymouth before switching to GDM, leaving the bootsplash on. And still no bootsplash on shutdown. Seems like there's more configuration/tweaking to do.