I think it grew out of Berlin rave culture (retch!), but it might be valuable as a mobilization tool for the Bush visit.
Individuals will establish meeting points in their own neighborhoods; parks, cafes, notable intersections, etc...
As multiple small rides progress toward U of P, they will likely converge into larger groups eventually massing as one.
The strength of such an approach is that with many smaller rides, the popo will be unable to harass them all, if any. Focussing the meetings at the neighborhood level will encourage people who would otherwise not ride CM (or even ride their bike [or even got to the Bush protest in the first place]) to attend.
As some IMC readers may know, I have sworn off CM. This decision was made due to my lack of faith in CM's ability to self organize. If massers opt to apply the Star Mass approach, I will be pleasantly surprised.