Adam Dachis put up a really good article, one certainly worth a read.
Mosey over to Lifehacker and take a look. Strongly recommended.
Interesting read but there was no mention of using, except the part 'I love goats', whole sentences. Caps, spaces, punctuation marks etc. For example, recently yahoo accounts were hacked and I had to change my password. Six words in a sentence, grammatically correct and easy to remember. May not be impossible to crack but it will give you a really big headache.