Depends on the content. If you're dealing with broad timeless subjects dating isn't a big issue. You could read an article 50 years old dealing with male/female relationships and get some value out of it. If you're dealing with technical issues, or any subject that moves fast, it's more than a little irresponsible not to date your work. I've personally hosed multiple Linux systems trying to follow old out of date HOWTOs. I know better now of course but I still have to filter through hundreds of outdated results for almost any technical search I do these days.