Introduced in Ubuntu 7.10 was install-time encryption support where using the alternate installer one can fully encrypt their disk in an LVM using dm-crypt. Unfortunately, the Ubiquity installer in Ubuntu 8.04 continues to lack LVM and encryption support, but using Ubuntu 8.04 Alpha 6 we have looked at the performance cost of this encrypted configuration on Ubuntu Linux. Rather than looking directly at the disk read/write overhead caused by the encryption process, we have provided some benchmarks to see how the real-world performance is impacted in both gaming and other desktop tasks.

http://www.phoronix.com/scan.php?page=article&item=ubuntu_hdd_encrypt&num=1