Default Settings in Mac OS X How can I reset all settings for the system preferences in Mac OS X? I'm using lion.
I found this post, from the official Apple Support Forums, regarding the exact question, after a quick google search on the topic:
Official Apple Support Forum


  I have been able to accomplish this via the following method. I may
  not be the best idea given it deletes the account while logged in, but
  worked for me.   
  
  1) Do all of the necessary installations, etc. just as under Snow Leopard, using your setupacctname account.   
  
  2) Once that is done, BEFORE restarting in single user mode:
       sudo su
       dscl . -delete /Groups/admin GroupMembership setupacctname
       dscl . -delete /Users/setupacctname
  3) Reboot into single user mode (Hold Command-s at startup)
  4) Check the filesystem: /sbin/fsck -fy
  5) Mount the filesystem: /sbin/mount -uw /
  6) Remove the setupacctname directory: rm -R /Users/setupacctname
  7) Remove or rename .AppleSetupDone so you get the language choice

 cd /var/db/
 mv .AppleSetupDone .RunLanguageChooserToo   or

 rm .AppleSetupDone   

  
  8) Delete miscellaneous files (unnecessary, but useful if you're imaging the drive):

 rm -R /Library/Caches/*
 rm -R /System/Library/Caches/*
 rm -R /var/vm/swapfile*   

  
  9) Shutdown or restart