The only standard we should set is a minimum length that is not too short. Something like 8 characters minimum. I don't care if you use only number or only letter, use whatever you want, it's YOUR security after all! The longer the password, the more likely it is to be unique!

My password has been letters + numbers at the end for a long time and I know it's secure because it's not a common word or numbers that have to do with me. No capitals, no punctuations, only lowercase letters and numbers. When a website forces me to use other letters in my password, I keep forgetting it and I am forced to use "Lost my password" all the time, which makes me want to use that service less and less.

Were you inspired to post this by today's XKCD comic? Link : http://xkcd.com/936/