Earlier quoted context omitted.
It worked well in the past. They made significant improvements to it. However, it's not as well-suited for multi-datacenter usage. For example, they needed another replication layer. I think they're working on a current system that will replace memcached, and it seems to be causing some consistency problems...
Do you have any additional details about this possible memcached replacement?
I do, but I'm not sure if I should say anything about it. Sorry. It's not open-sourced (yet), like everything else is.