Completely painless.
1.) Backed up everything via My Backup
2.) Switched to stock ROM in SafeStrap
3.) Booted up, uninstalled SS, updated SU, installed Voodoo and protected root
4.) Rebooted into recovery, installed from zip
5.) Rebooted, watched it go through its spiel, went into Voodoo to restore root and checked SU and all's good!
Now I'm just letting My Backup do its thing and I'll spend another hour putting my phone back the way it is...but first impression is that JB really is an improvement
Thanks to everyone who did this first - for your feedback and suggestions - and for Sam for all of his tips, tricks, insider info, and for sticking around to help when possible!