Have you ever thought what happens to your data if you lose your machine or give it for repair? Remember your data is your identity. Its very important to encrypt your hard disk.

On Ubuntu you can enable home directory encryption by default. In case if you find it difficult or you have many portable harddisks or use any other OS then use TrueCrypt. It is an open-source, transparent, on the fly encryption which is very easy to use. It works on all the platforms. Portable versions are available too.