It was reading this blog post that first got me thinking about this topic, but it seems to me that on most blogs, posts that are older than a month generally fall into two categories: those rare few that are popular and will actually show up in search results long past the time when they were relevant, and those that disappear forever. They're still there, but nobody will ever view them as they become buried under a deluge of newer posts. Both of these situations are a problem.
The popular posts that show up in searches have been a particular thorn in my side of late. I'll search on something or other, find what at first appears to be an excellent solution to my problem, and then discover that the post in question is four years old, which is an eternity on the internet. The post is referring to a bug specific to Windows Vista when I'm interested in Windows 8.1, or the discussion forum references a website that hasn't existed in two years. Even worse are the posts that don't have dates - finding out whether the information is relevant is a chore in itself!
On the other side of the coin are the posts which may be interesting, but which get buried. On many topics that aren't date dependent, posts written in 2003 might be wonderfully insightful or particularly relevant, but there's no way to locate them. And Wordpress/BlogSpot/Blogger software doesn't do a great job of organizing archives. In this respect, I'm very happy with the way I've organized my own blog archives - by year and topic.
I don't know how soon some kind of standard might arise to combat these issues. My first thought was that HTML5 might be expanded to add a relevancedate attribute to the article tag. If search engines recognized such a thing, though, you can be sure that it would be misused in pursuit of better SEO. So in the end, I don't know how to solve the problem. In the meantime, I'll be happy with the structure of my own blog and leave it at that.