Patrick's advice about taking dates off is spot-on for optimizing conversion rates on key pages. I've taken dates off of my most important evergreen resources.

There's sometimes a happy medium - you can deemphasize the date with CSS or by putting it at the bottom of the post.

Here's an example of a blog-style post on my site: http://joshkaufman.net/malinvestment/

People who want to find the date can find the date. People who aren't looking for it aren't likely to see it.