Unlike adding a password, encryption is a far superior way to protect your data. But depending on how complex your encryption method, etc... there is actually a penalty that you have to pay. For instance the more deep you encrypt (using the most complex algorithms, etc) it can actually slow down your HDD or PC in general.
But most of the time, depending on your activities on your PC, etc... you may not even notice it (slow-down). If you want more security then you can purchase a HDD with built in encryption at hardware level which also helps to reduce the CPU involvements thus making minimizing the slow-downing (in some aspects). Since the encryption does not depend on your OS... your data will be protected even without an operating system as well.
Anyhow, for some reason say that your Ubuntu 11.04 Natty chose not to boot so you had no choice but to reinstall it, then how can you recover your encrypted "Home" or partitions in that matter?.
Well in that case, there is a command line tool called "ecryptfs-recover-private" that let you mount any encrypted directories with ease!. You can use your Ubuntu Natty's live CD and boot into the desktop and mount the partition where your data is at (unless Ubuntu live CD didn't mount it automatically) and open your Terminal and issue the below command.
sudo ecryptfs-recover-privateIt'll ask for several validations... just follow the instructions on your screen and get your data back!. If you want a more through and easy to understand video... then the Ubuntu sever developer Dustin has even released a video showing how to do that (below). Enjoy!.