As my upgrade to Ubuntu 10.04 ended with a kernel panic and I needed to have a running PC for work, I ran a new installation.
Instead of the proposed partitions, I installed Lucid over the existing Ubuntu installation. For the home folder I chose the encrypted settings, as it was on my former installation. Now it is important to chose the same username and password as it used to be because the key to unlock the home folder is generated by those values.
The installation was finished within 15 minutes. And my old (encrypted) home folder was mounted without any problems. This is an installation as it should be.