Yes. We stick with memcached. Every node in our cluster has an uptime of over 3 years handling up to 5000 requests a second so we're quite happy to leave it. In fact it's the most reliable thing I've ever seen I think.

Redis looks nice but I suspect that it may be easy to lean on it too much for functionality. We were looking at it for a couple of tasks but haven't found much motivation to move yet.

With that track record, there has to be a very good reason to switch.