I am not sure if what happened to me this morning is exactly the same as what is going on here...but i solved it by downloading disk warrior 4.2 and running that while booted from a separate external HD.
I walked into work and my computer was hung...so i fussed around and it seemed to be ok. I then tried to move a file into my applications folder and received a message that i did not have permission to do that. Logging out and then logging in and my password did not work...nor did logging in with any other accounts on the exchange server.
I panicked because i had just read about this problem with 10.6 last night.
I installed 10.5 onto an external drive and booted from that...and could see my original volume but most of the folders were empty...again panic.
I was able to copy my "user" folder to the external drive...and then i ran disk utility to repair disk and it would not repair and said something about "invalid key" and then would not allow my to mount the volume...i was just about to wipe it when i thought i would try disk warrior...
downloaded that and ran the rebuild and everything is back working perfect...knock on wood.