I think this is the real key. Sentences as passwords are really hard to crack as long as you choose a reasonably long sentence that you can remember easily but

I think this is the real key. Sentences as passwords are really hard to crack as long as you choose a reasonably long sentence that you can remember easily but is not overly simplistic or obvious, and if you include a few typos or non-standard capitalization and/or punctuation it becomes that much more difficult to crack. A sentence is the only way you'll get normal users to memorize a password > 6 chars. I think a sentence is much better than what most people end using, which is a personally significant word (like a child, spouse, or pet's name) + a brief personally significant numeric suffix (like birth year).