Technically, it is not SUPPOSED to be progressive. But, for many, they become more and more aware of symptoms as time goes on. Also, as symptoms can wax and wane, who's REALLY to say whether they get worse or not, except the one experiencing it.
From a medical point of view, though, it is not considered to be a progressive disorder. But then again, when medicine can't even find a way to convince all of their members to even believe there IS such a thing as FMS, it's hard to have faith in their judgment when they say this non-existant disorder does not progress.
So, pick your take!