What is the memcache report screen telling me?
Those are operations on your memcached server.


Sets: Data placed into cache by sets/second; by absolute number (by % of total commands); and a display of total number of commands. Sets are expensive (it represents needing to retrieve from your DB or other slower data sources) so you want this to be as low as possible, relative to gets.
Gets: Data requested from cache by gets/second; by absolute number (by % of total commands); by absolute number of cache retrievals (by % of total gets); by absolute number of cache misses (by % of total gets). Gets are the entire reason you employ memcache (to retrieve from fast memory rather than a slower disk/network) so you want this to be high as possible, relative to sets.
Counters: The number of increment/decrement operations performed on memcached counters.
Transferred: The ratio of read to written data. Since it's in absolute data amount, it gives you an idea of how much you're saving in reading from slow disk/network storage.
Per-connection average: The average amount of data and memcache operations made in a Drupal connection by gets/sets. The should give you an idea of how much memcache is employed on a Drupal request.
Available memory: The amount of memory used / available on the server. This is another metric showing how much you're utilizing memcache.
Evictions: The number of evictions or cached data removals from your memcached server.