I find myself not working memcached (and variants) into new designs these days, mainly because with Cassandra on the backend, there's no point -- better to spend the money on the Cassandra machines and let it manage the caching, in-memory indexing, and log-structured writes.

Memcached in that scenario just adds network overhead, devops complexity, and increases the number of things that can go wrong.

For the times when Cassandra is overkill, I still end up using Redis -- with the Lua stuff, it's ridiculously flexible these days.

Still, McDipper (and Twitter's fatcache) both look cool, and I'm glad people are thinking about SSDs as something other than faster "disks".