Comment 2 for bug 353446

I'm sorry, but an encrypted home directory and gdm-autologin are two features that are simply incompatible.

We handled this in the installer by allowing you to only one of 3 different options:
 1) auto login (no password)
 2) login with a password
 3) login with a password and decrypt your home directory contents

I believe this should be solved in the gdm Login Window Preferences -> Security tab. The 'enable automatic login' option should be greyed out if the user has an encrypted home directory,
 $ mount | grep "on $HOME type ecryptfs"

seb128, I'm going to wishlist this against gdm.

:-Dustin