Permissions of "Macintosh HD" changed, no encountering spooky problems

Question

I was probably on another star when I not only added another user (my new MacBook) to the "Macintosh HD" user list of my iMac, but also went via the action menu to apply this new user to all subfolders. I did all this because I wanted to have access to all documents on the iMac via a network connection from my MacBook... Maybe I overshot a little bit... Even the MAC OS X warning message -- "This cannot be redone!" -- went by unheard... OS then took a break of at least one hour and changed all subfolder's permissions by adding this new user with write&read rights.
But not only that:
Now I'm facing spooky things. First of all: TM was unable to do a backup because the drive was "locked" by a different user (which was neither the admin of the iMac nor the new user I created). My response: I used the disk utility to reformat the external drive and solved this problem with this rabiat method... Second, Mail wouldn't allow me to move messages in my subfolders. I found a threat here in the Apple forum that seems to be a solution. Third: My fonts seem to be locked and are replaced by other fonts in documents.
My question is very broad and is an invitation for all experts on this forum to explore the best practice: Is there a smart way to turn back time (not via Time Machine) to get permissions back to normal. What happens if I save all relevant files such as fonts, mails, iPhoto, iTunes etc. and do a complete reinstall of the iMac?! Will this radical solution solve my problem which seems to have dimensions I'm not even totally clear about at this point?? I only realize that everytime I open an application or a file, I encounter a new surprise...

Answer 1

I created a new user, applied this new user with "write and read" permissions to "Macintosh HD" and used the action menu to apply this to all subfolders (which means to all folders of the iMac).
this has completely hosed your system beyond repair. do a full system restore from time machine. boot from the leopard install DVD and go to Utilities menu-> restore system from backup. In the future, NEVER EVER, under any conditions use "apply to enclosed items" button on ANY system created folders and the system hard drive. that includes any folder you didn't make yourself such as your home directory, your documents folder, the Applications folder etc.