Using a password manager has a good side, of allowing you to set different passwords for different applications and services. This is increasingly important because many online services are compromised and user accounts (and passwords) can be used by the attackers. If you use the same password on other services, those can also be abused or misused by the criminals.
Of course it is less convenient to create, use and store different passwords. More importantly, if your vault is broken into (someone steals your master password), all of your passwords are also compromised. So any time you use a password manager, the master password should not be easy to guess.
One way to create a strong password is to use a series of unrelated words that you can easily remember but would be hard to guess. Example: purple bird 9756 ham swim — picture a purple bird flying over a swimming ham, and pick some numbers like the street number across from where you work. Diceware is a convenient low tech way to generate very good, very strong passwords. More details on their FAQ page: http://world.std.com/~reinhold/dicewarefaq.html#login.