Not too long ago I sent out a question. I asked people when, and why, dates were important to them on blog posts. The responses were revealing, both for what they did, and did not contain.
There are some situations where having a date on your blog posts is obviously needed. If you write about anything techy you absolutely need them. I come across tons of sites with perfectly good code examples, that have been obsolete for years. Ditto for how-to's related to software and operating systems. The other place where dates are critical is anything related to news or politics.
Basically, if you've written something that will be used as research material later on, you need a date. Everyone seems to agree on that. But, what about pieces where the passage of time really doesn't have much of an effect. For example, I wrote a post about a paper-based task management system. Read it today, read it two years from today... it doesn't impact the usefulness or relevancy of the content at all. And that was the basis of my questioning. If you had a blog filled with posts like that, would there be any real value in including dates on the post?
The responses were overwhelmingly "YES", but not for the reasons I'd expected.
Freshness and Precision
While they used different words, everyone was in agreement that an indication of freshness was very important to them. Sometimes, it was just to help them know if the blog had been abandoned or not. More often, it was simply to know if the information in the posts was still relevant or not.
What was interesting, was that when pressed for details, almost everyone claimed that a simple freshness indicator (e.g. "three months ago") wasn't sufficient. They claimed that they needed to-the-day precision. They claimed that having this level of precision allowed them to compare it to what was happening in their lives at the time; they could look compare the date to their calendar, and see what they were doing then.
These claims seemed... suspect to me. They felt like the type of answers people give when they're trying to explain something they've accepted as true, or necessary, but have never actually thought about. Like, the idea that going out in the cold will lead to catching a cold.* So, I pressed for details. I wanted someone to give me a real world situation when they would look at a date on a blog post and actually do what they claimed. When would they ever compare the date of one to what was going on in their lives at that time, or to what was going on in the world at large at that point. The response, was a resounding silence.
As far as I can tell, if you exclude the types of posts where dates are obviously required (news, politics, content that will become obsolete) no-one actually needs dates with any real specificity, but because everyone believes they need them, their absence makes them uncomfortable, or at the very least, slightly annoyed.
I believe that relative dates are a much closer match to what people need, and much easier to actually use. "Three months ago" translates quickly to "recent, but not too recent", whereas 5/24/12 requires you to figure out what month 5 is ("let's see that's...May"), compare the day of that month (24) to the day of the current month ("Are they the same? Is that one earlier in the month than this one? Does that make it more time or less, and is that enough to bother worrying about?") before you can actually leverage the information in a meaningful way. But, what we need, and what makes sense logically, isn't always what we want.
I believe that Kirk's proposal of "mid-June 2011" is probably the best compromise between usability and need. It's easier for a human to parse than 6/15/11. It feels much more useful than "over a year ago" or "15 months ago", even though once you get that far from a dates post your true need for even to-the-month specificity is doubtful.
With that said, the more recent something is, the more precision seems to matter to people. So, you could probably improve on Kirk's suggestion by a building a system where dates are written with to-the-day specificity for one month, and then switching to "early May 2012" style dates after that.
When pondering dates in blogging, context is everything, and many, if not most, blogs have posts from multiple contexts. Hardly anyone writes a blog where the value of each post is unaffected by time. With that in mind, a blog's posts should be dated using a method that supplies the maximum level of precision required. If you write a blog of fictional stories, but occasionally comment on news that affects writers you need to-the-day precision, either that, or use a different level of precision on every post, but really, no-one wants to go through that much trouble.
* As it so happens, it's probable that being exposed to the cold for a while will increase your odds of catching one. Some scientists did an experiment where they had some college students stand in buckets of cold water for a while, and compared which of them got colds soon afterwards. The kids who stood in the cold water got more colds than the kids who didn't. I just wish I could find the research again...