I did brick my skyrocket by mistakingly choosing "Phone" instead of "PDA" in Odin application. when the Rom finished loading the phone rebooted and shut itself down and I wasn't able to turn it on anymore. Even when I tried to bring it to life with the USB jig it didn't work either. So yes, the phone can be "permanently" bricked, at least to the point where you wouldn't be able to fix it without special tools. There is a guy though who can fix these kind of bricks (he's got a video on youtube) and he sells kits also if you want to fix it yourself but its very expensive (around $200 I think) and requires opening up the phone and soldering skills.