I bricked trying to download the Cognition ROM on a rooted Eclair. I'm not totally sure how it happened, but I would not be surprised to learn that I did something totally wrong. lol
I thought I had Cognition loaded properly- it rebooted to a stock looking Touchwiz OS with pop up after pop up of error messages. It was a mess. I had to yank the battery and spend the rest of the day going back to stock, rooting and loading/side loading all of my apps back on.