In defense CORP; it is a bit dorky, but look around the next time there are a bunch of us together; not exactly inappropriate.
More seriously, I like the fact that it is more original and creative than the -AMBA/-ORBA names. It doesn't take that much effort to say, "CORP, the local IMBA chapter," if you are looking for more clarity. I also like the idea that it doesn't have Mountain Biking in the name, so that it doesn't exclude trail-runners, snow-shoe-ers, and other non-wheeled users of the trails, who are potentially good partners if we wanted to reach out to them. And I don't think the ten or fifteen years of using the name should be discarded lightly; maybe we don't do the best job of getting our name out to the masses (which is probably not the fault of the name), but there are quite a few people who do know it, some of them in important positions, and that is something that would take time and effort to re-establish.
I do think the P should be silent, as in Army Corps of Engineers. Then it would really be confusing.