From a longer article at lifehacker.com …

Assuming the hacker has a reasonably fast connection and PC here is an estimate of the amount of time it would take to generate every possible combination of passwords for a given number of characters. After generating the list it’s just a matter of time before the computer runs through all the possibilities – or gets shut down trying.

Pay particular attention to the difference between using only lowercase characters and using all possible characters (uppercase, lowercase, and special characters – like @#$%^&*). Adding just one capital letter and one asterisk would change the processing time for an 8 character password from 2.4 days to 2.1 centuries.