Who doesn't know what a Hula Hoop is? Who, of a certain age, never played with a slinky? When the Baby Boomers were kids nearly everyone collected stamps. In my neighborhood there were two different kid organized stamp clubs, created and administered by ten year olds. We were very adult in our social organization skills, spending enormous amounts of time on such matters as by-laws and rules and schedules and very little time trading and discussing stamps. Weeks were spent on discussions of whether we would admit girls to our august proceedings and the dispute would have continued to this day if it wasn't pointed out to us that there were no girls who wanted to join.
Philately was pervasive among children of the baby boom era. Today when I meet a contemporary and tell them what I do for a living I often hear about their childhood collection.They know about plate blocks and First Day Covers and the Scott catalog. Many ask me what an Inverted Jenny, the Lady Gaga of prepubescent 1950s philately, is worth today. It wasn't just stamps though. There were toys (like skateboards and Hula Hoops) that united our generation. Today, there is only entertainment and sports. The shared experience of Harry Potter will be what our kids remember about their youth.
Serious philately has always been a niche attraction. There are as many APS members now as there was 40 forty years ago and even though the population of the United States is larger one couldn't really be a serious collector in 1970 without belonging to the APS whereas today membership in that society is largely superfluous to buying and selling stamps. I don't think the hobby is in danger and large numbers of Baby Boomers are coming back, as predicted, to the hobby of their youth. But stamps and stamp collecting as a shared generational experience is something that we will probably not see again.