I want to pass along my experience with a seemingly unrecoverable soft brick in case others experience this.
My phone has been on Eclipse 1.3 with PBJ 0130 pretty much since they came out. It has also been on the EXT4 file system since the EE4 days. Ran great, fast, no problems until 2 days ago.
I had a random reboot occur just as I was receiving a text message. It then went into a boot loop mode. No problem, I thought, I just went into CWM and cleared cache and dalvik. Still stuck in boot loop, so I did a data wipe. At this point I got the message about the cache volume not being mounted. Mounting it only worked once upon entering CWM, but then would dismount when I tried to clear it. Same thing every time I reentered CWM.
Long story short, I went through complete ODIN restores of EP4, EE4, and ED2, and used the PIT file with each of them. Each time, the phone booted into the system restore and complained of not accessing cache directories. I did get past that on ED2, but it went right into another boot loop. Could not get any further. I repeated these flashes using the Samsung PSTlite utility. Same results.
Last thing I tried was to ODIN CWM again and used imnuts RFS format utility (from the Infinity ROM thread). Same problem. CWM could not format the cache. At this point I gave up, ODIN'd EP4 w/PIT, and took the phone to the Verizon store. They took one look and ordered a replacement. It came with all new accessories, BTW! Bonus.
Anyway, I have a thought that the ext4 format left something behind that was not recoverable after extended use. Trparky mentions this as a potential problem on his Droid Charge knowledge base (http://www.toms-world.org/android/page/whyuseext4.html
). I never really noticed the warning anywhere before, but will not be using ext4 on the new phone as a result.