Quick question to all you folks: does including the date in a blog article's permalink affect rankings? For example, here's an article with the month and year, as well as the blog title: http://www.ayzanyc.com/blog/2012/12/difference-between-hot-chocolate-hot-cocoa/

Is it better to omit the date and just put the blog title?

Also, if is better to avoid using the date, is it worth it to change the link structure of our previous articles (given that the URL will now be different), or should we just focus on future articles?

Thanks ahead of time for your advice.