Why on EARTH?!? would _ANYONE_ run CDP at a MAE or any other exchange point?
You would be suprised at the large number of folks who've got CDP enabled at the exchange points -- Ironically, we enabled it to get a sense of what other IOS versions were running on our peers routers prior to a code upgrade to fix some issues that were affecting us.
Especially given the congestion, and other problems at the MAE's, why run a protocol to discover other Cisco's you have to explicitly configure peering sessions with anyway? If someone can explain a reason not to turn off CDP at an exchange point, I'm all ears.
Given that its on by default cdp needs to either be turned off completely, or disabled for a particular interface, folks probably just leave it on. I highly doubt CDP contributes to congestion problems with the little amount of traffic it generates - Although if you've ever looked at some of the traffic at the Mae's you'd be sickened by all of the other things floating around. I suppose another eason to disable CDP in addition to disabling any non-essencial traffic and/or processes would be for privacy.