Using the memcached_set_behavior function and setting the MEMCACHED_BEHAVIOR_NUMBER_OF_REPLICAS to some integer you are ensuring that multiple copies of the stored values exist throughout your memcached farm.
My only issue was that I am using python-libmemcached to access my memcache servers from python and the 'replicas' behavior has not yet (as of 0.17.0) been incorporated. So using I had to patch the sources (RPM package is available on OpenSuse Build Service, patch is attached).
>>> import cmemcached as memcache
Of course, if you set the data on 1 server only it wont be replicated. Never the less ,this simple replication system opens a number of opportunities for some of my projects where I use memcache as a 'shared' storage between processes.
Warning: memcache does not have any security mechanism embedded (access,confidentiality...), use it only on trusted networks.