Imho Ubuntu has a serious design flaw in it's implementation of ecryptfs.
Imagine following situation:

1. You install Ubuntu using the alternate cd, create a separate partition for your /home and encrypt your home.
2. After some time you decide to reinstall Ubuntu (eg a fresh install of a new release) and obviously decide to keep your /home.
3. You log in and find out there's no way to access your previously encrypted data.

This is what happened to me. Somehow, during install, I seem to have missed (read: I don't remember seeing) the warning message that tells yo to print your mount key. After logging on to the new install, and talking to the ecryptfs people, I found out, it needs files located in ~/.ecryptfs. Nothing special it seems, as you have kept your /home, but... In Ubuntu ~/.ecryptfs is a symlink to /var/lib/ecryptfs/$user, which you obviously didn't keep. This, as far as I'm concerned, is a serious design flaw, that completely denies user logic of keeping /home on a separate partition.

One very important lesson that I drew from this: if you use an encrypted /home, and haven't printed your mont key yet, do so now!