Upgrading to OS X 10.5 'Leopard' with stuff in /home
Upgrading from OS X 10.4 to 10.5 gave me a slight heart attack when I realised that my /home folder with 15 years worth of web development and cvs/svn repositories had vanished and been replaced in my sidebar with an empty folder and a snazzy new 'protected alias' icon.
Thankfully, searching the Apple discussion forums revealed that it wasn't a huge data-loss bug, but that I just needed to uncomment a line in /etc/auto_master
http://discussions.apple.com/messageview.jspa?messageID=5665487&stqc=true
Hopefully, this will get the solution into Google's results so other people don't get bitten.