Peering links between backbones (like Level 3 and Verizon Business) are supposed to have equal ratios. Peering between content providers and end-user ISPs don't care about ratios.

I'd say that wmf addressed it already. Peering points with one side being primarily consumer services are always going to be unequal due to the nature of the end user and the ways in which consumer ISPs provide bandwidth to their customers. Lots of download, and very little upload speed as an example. As such it's nearly impossible for many peering points primarily used by consumer services to use an equal amount of traffic on both directions. Both sides of the agreement know this and it's still usually in both of their best interests to peer settlement free.

I'd say a lot of the peerings at DECIX and AMS-IX.