Today a though came in my mind. For example when you post in your blog the page will appear something like this : yoursite/year/month/your-post.html.Ok if we are in 2007 the post will rank high in search engines, but in 2008 or 2009 your post will be the same ? I don't think so ... so how can we keep our high earned rankings over time ? Thanks
The date does not have such a large impact. Its the content itself and your blog structure that matters.
Think of a date to be more like a number that makes sure your URL is individual. If people keep referring to the page that you wrote today in 2008 then it will remain popular with search engines.