I would suggest that the largest percentage of flapping prefixes in the global routing system belong to prefixes longer than /19.
Hence the convention to damp differently for different lengths. See one of the foils in http://www.psg.com/~randy/970210.nanog/, which suggests that we over here start following the European lead on this.
Is the route computation of a /8 prefix flapping once a second any different than a /24 flapping once a second? If /8's are "naturally" more stable, then why allow them to flap more before dampening them? When dampening was first being rolled out I remember one of the early networks that got hit was PSI's net 38/8. Treating flapping prefixes differently based on length has more to do with how many people scream when prefixes covering a large amount of address space get dampened than the impact of the route flap of an individual prefix on the router. Although most folks have permanently filtered it, isn't 1/8 still the flappiest prefix of all. -- Sean Donelan, Data Research Associates, Inc, St. Louis, MO Affiliation given for identification not representation