Shows people you recently spoke with higher up on the AutoComplete list (when typing in a name to message).
Changing this setting
In-game, type the following
/console autoCompleteResortNamesOnRecency setting
Alternatively, you can exit wow, open the Config-cache.wtf file, and add the following line:
SET autoCompleteResortNamesOnRecency setting
Patch 3.3.2 (2010-02-01): Added