Actually, this is more of a recommended practice than a tip... . While conducting various web searches today, I came across a magazine issue that featured special coverage of the European migration debate. Since I was in the midst of preparing a post on Europe, I took a closer look to see if it was recently published. I dutifully checked the cover - but no date. I checked the publication information on p. 5 - again, no date. I looked in all the obvious places, but as far as I can tell, the magazine provides no indication of when it was published. I finally went to the web site, located the relevant page that posted the issue, and learned that it came out in June 2012.
I don't mean to single out this one magazine. I constantly come across working papers, reports, web pages and other resources that don't include dates on them. And it's certainly not a new phenomenon, since all style guides include instructions for how to cite materials when no publication date is provided. But since I focus on "current awareness," dates are generally the first thing I look for, and it's frustrating when they are nowhere to be found!
So a plea to all authors/publishers: Please put dates on your content, preferably in an obvious place! Your readers/users will appreciate it!