Everything on the net should be dated - iameven.com
Talking about obvious things that are obvious. Dates should be stamped on everything that is published.
It annoys me, to come across any web resource and not know when it's from. Something so basic, for a computer, as time, should almost be a forced default. Like a part of the standard. If something is written 5 years ago chances are that something new has happened since then. Especially in technology. The web is only getting older and it's not like there's less content coming.
The SEO (Search Engine Optimization) people seem to be quite clear on not using dates in your URL's at least. More or less to confuse Google in to believing your content is more relevant/fresh than it is. And in some cases I can agree. Old does not equal irrelevant. But the only reason they seem to be forcing this guideline is to get an edge on the people who are dating their content. If not exactly dark, I find it shady.
If you don't want dates in your URL, that is fine, but consider at least to write it, clearly. Not long ago I saw a report on cancer research spreading through the social networks, from 2006. I'm sure this gave people hope (hence the sharing), because it was not obvious to see that the information was not recent. There where no further reading on those studies, so I'm not sure if they ever got any way with it.
<time datetime="YYYY-MM-DD HH:ii:ss">Day in Month, Year</time>
It looks like w3 feels the same way. I'm exited to see how browsers and plugins will take advantage of the element. Hopefully Google will start punishing pages with no published date.