This question is hardly linguistically earthshaking, but I read something this morning where the writer disagreed that the Atkin's Diet was a fad. She said that it had been around for 30 years, and a fad is shortlived. Indeed, AHD says that a fad is "great enthusiasm for a brief period of time." While 30 years is a long time period, in the scheme of things it's not. Yet, if everything were measured in the scheme of things, then everything would be a fad! How long does a fad have to be around before it's no longer a fad?

As long as we're talking about fad, AHD says that it is "possibly from fidfad, fussy person, fussy, from fiddle-faddle" Fidfad? I couldn't find that anywhere.

While it may have been around for thirty years, the sudden rise in popularity, then a sudden collapse (Adkins is now bankrupt, I heard) smacks of faddishness to me.

It's all relative. Given the age of the earth (outside of Kansas, anyway) and the percentage of time mankind has walked upon it, one might say that the human race is little more than a fad.

I still think 30 years could constitute a fad. This makes me think of those movie commercials that say "the funniest movie since last month" or some such nonsense.