One SEO consideration that can be overlooked is having the same content be accessible by multiple urls on your site. This is called duplicate content and your site can be flagged and disappear from Google or other search engines.

If you're using Drupal with Clean URLs and ‎Pathauto‎, consider the following:

http://www.example.com/blog/2010-03-10
http://www.example.com/node/256