I had JP6 running stable for a few days (since Saturday). Last night I installed Voodoo 5 preview for Froyo and it went fine, had the desired effect etc. This morning I installed Superuser and Busybox to take advantage of the root, and after a reboot my phone refused to boot, even after cache wipe and factory reset :-(
Trying to download JP6 and Odin at work now...
I tried to get into reboot mode this morning and had that awful sinking feeling when I saw for the first time the brick icons. Thankfully I was able to get into download mode and just flashed the JPM tar file in Odin.
I'll have to look up how to uninstall the Root access and try the one Lokhor has mentioned.
I feel for you trying to breathe life back into your phone while at work.