There are several questions regarding plymouth :
1.Is it safe with Ubuntu Maverick 10.10?
2.Is it reversible?
3.If thing goes wrong , what are the effects?
4.Will it clash with Burg??
I think there are a lot of variables when it comes to plymouth (specifically the graphics card and what drivers you're using).
I'm using an Nvidia card with the proprietary drivers. Initially plymouth didn't work and it would fall back to the text based boot screen. I came across a script that fixed it and let me select the resolution just barely today and it seems to work great.
At that link you'll also find a script to reverse the effects of the script.
I wouldn't expect it to conflict with Burg since (I think) the bootloader is unrelated to plymouth (being started by the OS and not the boot loader ... could be wrong though).
In my experience it has been completely safe.
I can confirm that BURG and Plymouth do not clash in anyway on Ubuntu 10.10. I've been using it with the refit theme, and it works fine.
Burg and Plymouth have problems with a Nvidia drivers on 10.10. Messed about with it for hours going back to goodod unsightly Grub amazed that it hasn't been tested by someone.