Cool story bro time:
I bricked my phone trying to downgrade from CyanogenMod 7.1 to stock DL09 on my Fascinate (SCH-I500). The handset would never boot past the Samsung logo.
When I went into the Android System recovery (ASR) tool, it would spit out "can't mount /dev/block/stl11" errors. Trying to restore using the sdcard:update.zip returned a "can't mount /dev/block/void/179:9" error.
When I pulled the battery and attempted to enter download mode by holding the volume key down, the handset never made it past the Samsung logo. I could only get to download mode by entering the ASR tool first, rebooting, and then holding down the volume button.
Odin 1.3 would see the phone on COM5, but when I attempted to apply the tar.md5, Odin would return with the error:
<ID:0/005> SetupConnection..
<ID:0/005> Can't open the serial(COM) port.
Solution:
Pull the battery and keep it out. Power on the phone with the USB cable connected (it'll pull power over the cable). Holding the volume button in the down position, it will go directly to download mode and Odin 1.3 will have no problem applying the .tar.md5 file.